I actually went down to a bike shop to try it on a bunch of frames. It's thin enough that the curve of a top tube doesn't actually make much difference. It's only 20mm wide, and, while there are some super-curvy high-end frames that I haven't tried (Van Dessel comes to mind), most don't seem to be a problem.
Super small frames can be a problem, though. I put one on a 46, (I think it was) and the seat cluster was so close to the back brake, there wasn't really room for the end of the bow. We're thinking about manufacturing smaller ones in the future, but for now, we have to stay focused to get the funding to do the first production run.
We've gotten a really funny and attractive suggestion to make a ninja scabbard for it so you can put it over your back for those who don't want to or can't attach it to their frame. I'm inclined to design a messenger bag attachment, too, and a couple of people have suggested tiny bows that are just super light and cover one wheel and the seat tube. So we're thinking about other options. But only focus will get us to the point where we can actually do any of it.
The price is going to be a barrier but not an insurmountable one if the lock works as advertised.
Yeah, the price is something we have to contend with. But if we can't sell it at this price point, we can't afford to make it. That's part of what's great about Kickstarter: you can find out if people will buy something before you put in your $37,500.