I got one on the weekend for use here in Germany, so far I am kind of mixed. Device came with 4.3 and updated to 4.4.2 without issue.
In principle the device (admittedly I refer to it as the hockey puck) is slick though in practice it is sluggish to navigate the menus and I find I switch more to using Screens to pick music that way (ESP as I am playing music I haven't listened to in a while). I'm shocked that it's not possible to switch CC on the fly going out of the movie to get to the Settings menu is a pain. Nor have I seen evidence of Subtitles, I have them on in settings but I've seen no way to turn them on/off on a video. The most annoying thing so far is that sometimes it simply fails to respond, be it asking to play a video or music it will simply spin it's activity indicator for ages doing nothing. The iTunes library it's connected to was active and the network wasn't congested so there was no sensible reason for it. ESP as it was easier to switch to iTunes and start it from there instead.
I'm still debating if I keep it, or wait to see what they might bring to the ATV3
Pros:
Slick
Tiny
AirPlay
Does 720p which my TV does
Gets the MacMini, Drobo, UPS and Printer out of the living room (which greatly pleases the missus)
Cons:
Only Digital out, means I need either a new amp or external DAC for music while Telly is off. Otherwise I need to leave our plasma TV on all the time to play music through it.
Sluggish to navigate (either the physical remote or via iPad / iPhone Remote app)
Closed Captions & it seems subtitles can't be turned on / off on the fly while watching a video.
Lack of track info (last played, play count) so need to remote into Mini to see when I last played an album.
(Not AppleTV but some implementations of AirPlay stop when app closed/backgrounded - looking at BBC iPlayer - which renders iPad useless while watching)
Sometimes doesn't respond when asking it to play something, it sits on the spinny icon for a while doing nothing.
[EDIT]
Video played via AirPlay are cropped a little, seen this on both Youtube app and StreamToMe. TV's res is 1360x768, and AppleTV is set to auto. So for instance in this video
http://youtu.be/VIUnvSguF0Q?t=1m32s the controls that appear on the map (LT and RT) have lots of space to the left and right of the controls and more underneath as well. But on the TV, the controls are snug on the left and right edges of the screen.
Indeed I get the same result when using the native YT app on the ATV :/ Even after forcing ATV output from auto to 720p 60Hz. I wish I could unsee this.
[EDIT 2]
Aha Setting the AppleTV output to 1024x768 (60Hz) interestingly makes things output correctly. I've compared the same video playing via Mac and AppleTV (swapping between the two HDMI outputs), paused at the same points and specific things are in the exact same place, and the same width.
[EDIT 3]
Okay. For video to play correctly I need to set the AppleTV output to 1024x768 but that messes up AirPlay mirroring. In that mode the mirroring only takes up a portion of the screen on the left and the bottom of the iPad screen (landscape or portrait) is cut off. Starting RealRacing 2 in this mode also doesn't work properly, specifically it won't go fullscreen.
To get mirroring to work properly I need to swap back to 720p, which is less than ideal.
Oh Fergal Sharkey.