I'm interested in the Keys To Go, haven't been able to try it yet, none in stock where I live. Is it better than the Ultrathin in general, and in the typing in particular?
Well, to be fair, I have the Mini Ultrathin, so my evaluation of it is going to be a little different than perhaps it would be from someone who has the Air version. The Mini edition is a very, very compact little keyboard, which has both strengths and weaknesses. It has very crisp keys and feels like any traditional keyboard, once you get used to the smaller size.
There were a couple of reasons I moved on from it: the outside is very slippery as it's out of aluminum; this wouldn't be as much of a problem if it were heavier, but it's so slim and light that I'd find it sliding across the table as I typed away on it. The size works against it too in that when you put the ipad into the groove it provides as a stand, the ipad is just too darn close for viewing comfort.
The Mini version also doesn't work
well as a smart cover. It doesn't stay closed on its own. I don't know if they've corrected that in either model since I first bought mine. It really needs either a strap around the ipad/keyboard "cover", or it should be kept together in a snug sleeve.
The Keys to Go isn't a full sized keyboard either. It's a good 2" shorter than the Apple Wireless. But it's a bit more spacious feeling than the Mini Ultrathin. It weighs almost nothing, and it's actually thinner than the Ultrathin.
The typing surface on the Keys to Go is different, to say the least. You're really typing on fabric covered mechanical keys, so it does feel a bit weird until you get used to it. It's not as easy to use as a more traditional keyboard due to the fabric texture and the very, very shallow keys--it's a bit easier to typo with than most keyboards I've used.
BUT: I got used to that pretty quickly. I do type a little more slowly on it so far--I've only put a couple thousand words on it, so I'd say I'm still adjusting. But I'm liking it a whole lot. It's definitely the most portable keyboard I've ever used, which counts for a lot. It's device agnostic; I'm using it with the Mini to type this up, but I've already tried it out with the iPhone, and it will be easy enough to pair with an Air (or the fabled iPad Pro, should that ever materialize!). It doesn't slide around when I type on it. It's rigid enough to use on my lap (with the ipad off to one side, upright thanks to the smart cover). And of course, I can spill coffee over it without having to worry about needing to buy a new keyboard, which is a huge plus over basically any other model.
I like it quite a bit. I think it's a touch over priced at $69, and I could wish for more color options. But I can see where this keyboard will be a better fit for my needs than any other I've used or even considered.
Hope that helps a bit!