Back in the iOS5 times, when evaluating the then-available high-framerate & slow motion recorders for the then as the only high speed viedo-recording-capable iPhone model, the 4S, I didn't really recommend Better Camcorder ($free with a 10-second restriction; unlock costs $1.99), because it was clearly weaker than the alternative, SloPro.
Now, exactly the opposite is true: the just-released, brand new version (1.7) of Better Camcorder is clearly better than SloPro with regards to making use of the brand new zooming-specific features of iOS7. And the in-app purchase unlock only costs half of that of SloPro.
Appstore update notes below, along with those of the latest version of SlowCam ($1.99), of which I'll also publish a detailed review (as usual, click the image for the original one):

For the moment, feel free to check out my quick remarks on the latter app at Digital Photography Review. In a nutshell: compared to SlowCam, Better Camcorder is much more versatile because it can shoot in any video mode, can (at least theoretically see my bug report below) en/disable the image stabilization but cannot export truly 30 fps footage ready for true slow-motion video upload. It will export native, raw 60 (iPhone 4S / 5 / 5c) / 120 (iPhone 5s) fps video to the Camera Roll, which means you'll need to do some desktop processing to slow it down by a factor of 2 or 4 by converting it to 30 fps. In this regard, SlowCam is much better.
However, when it comes to lossless zooming, the just-released Better Camcorder is the only AppStore app I know of to support making use of the lossless zoom in iOS7. (Please check out my recently-published Lossless Zooming bible for more info.) And it does it flawlessly. While other, not-yet-updated apps with zooming capabilities still use lossy zooming resulting in much inferior image quality at any zoom ratio, Better Camcorder does it losslessly (in the lossless range, of course). Let me present you a 720p30 video framegrab grabbed from a video I've shot with the, at 720p30, maximal available lossless zoom, 2.18x:

If you compare this to my 720p resolution chart shots made by my reference zoom implementation in the introduction of my above-linked Lossless Zooming bible, you'll notice it's of the same quality. No old-school, lossy digital zooming took place.
Here's a screenshot of the app in action while shooting the above 720p video:

Pay special attention to the zoom slider on the right. Below it, a label shows the current zoom level. As you can see, it shows 2.18, which, as I've explained in my Lossless Zooming bible, corresponds to the maximal lossless zoom factor when shooting at 720p. (Again, the above reschart shot was shot at this very zoom factor.) The zoom slider only lets you use lossless zooming, unless you specifically enable digital (that is, lossy) zoom in Settings (see the Digital Zoom switch at the bottom):

Problems, bugs
1, If you switch between resolutions and, in 720p, between normal and over-30 fps modes, the zoom slider will still allow for zooming using the lossless threshold in the previous mode. This means if you shoot at 720p30, which allows for a losslesss zoom of the factor 2.18 and, then, switch to 1080p, where the threshold is a lower 1.45, the change won't immediately be noticed by the slider. You'll happily shoot at 2.18, thinking the iPhone is still recording (almost) lossless, (almost) full-resolution footage, only to later find out that it was no more the case.
Pay attention to this bug. Basically, after some recording / setting change titles, the changes will be noticed. Note that killing and restarting the app won't help on the contrary, it'll even forget the previous setting.
2. Equally rushed is the Video Stabilization switch in Settings (see the center of the following screenshot):

It just doesn't work. All the test videos I've shot were recorded with the stabilization off, independent of the state of this switch.
Hopefully, these bugs will be promptly ironed out. In the meantime, only shoot with this app if you really don't mind the lack of stabilization (because, say, you're shooting from a tripod) and don't forget to pay attention to the zoom slider bug to avoid shooting with an already-lossy zoom factor.
Now, exactly the opposite is true: the just-released, brand new version (1.7) of Better Camcorder is clearly better than SloPro with regards to making use of the brand new zooming-specific features of iOS7. And the in-app purchase unlock only costs half of that of SloPro.
Appstore update notes below, along with those of the latest version of SlowCam ($1.99), of which I'll also publish a detailed review (as usual, click the image for the original one):

For the moment, feel free to check out my quick remarks on the latter app at Digital Photography Review. In a nutshell: compared to SlowCam, Better Camcorder is much more versatile because it can shoot in any video mode, can (at least theoretically see my bug report below) en/disable the image stabilization but cannot export truly 30 fps footage ready for true slow-motion video upload. It will export native, raw 60 (iPhone 4S / 5 / 5c) / 120 (iPhone 5s) fps video to the Camera Roll, which means you'll need to do some desktop processing to slow it down by a factor of 2 or 4 by converting it to 30 fps. In this regard, SlowCam is much better.
However, when it comes to lossless zooming, the just-released Better Camcorder is the only AppStore app I know of to support making use of the lossless zoom in iOS7. (Please check out my recently-published Lossless Zooming bible for more info.) And it does it flawlessly. While other, not-yet-updated apps with zooming capabilities still use lossy zooming resulting in much inferior image quality at any zoom ratio, Better Camcorder does it losslessly (in the lossless range, of course). Let me present you a 720p30 video framegrab grabbed from a video I've shot with the, at 720p30, maximal available lossless zoom, 2.18x:

If you compare this to my 720p resolution chart shots made by my reference zoom implementation in the introduction of my above-linked Lossless Zooming bible, you'll notice it's of the same quality. No old-school, lossy digital zooming took place.
Here's a screenshot of the app in action while shooting the above 720p video:

Pay special attention to the zoom slider on the right. Below it, a label shows the current zoom level. As you can see, it shows 2.18, which, as I've explained in my Lossless Zooming bible, corresponds to the maximal lossless zoom factor when shooting at 720p. (Again, the above reschart shot was shot at this very zoom factor.) The zoom slider only lets you use lossless zooming, unless you specifically enable digital (that is, lossy) zoom in Settings (see the Digital Zoom switch at the bottom):

Problems, bugs
1, If you switch between resolutions and, in 720p, between normal and over-30 fps modes, the zoom slider will still allow for zooming using the lossless threshold in the previous mode. This means if you shoot at 720p30, which allows for a losslesss zoom of the factor 2.18 and, then, switch to 1080p, where the threshold is a lower 1.45, the change won't immediately be noticed by the slider. You'll happily shoot at 2.18, thinking the iPhone is still recording (almost) lossless, (almost) full-resolution footage, only to later find out that it was no more the case.
Pay attention to this bug. Basically, after some recording / setting change titles, the changes will be noticed. Note that killing and restarting the app won't help on the contrary, it'll even forget the previous setting.
2. Equally rushed is the Video Stabilization switch in Settings (see the center of the following screenshot):

It just doesn't work. All the test videos I've shot were recorded with the stabilization off, independent of the state of this switch.
Hopefully, these bugs will be promptly ironed out. In the meantime, only shoot with this app if you really don't mind the lack of stabilization (because, say, you're shooting from a tripod) and don't forget to pay attention to the zoom slider bug to avoid shooting with an already-lossy zoom factor.