I've played a UC-1. It was spectacular. Construction was impeccable and polished. I couldn't find anything wrong; the attention to detail was unreal, like it was built in a laboratory. It's full and rich sounding, if not a little brash, something I attribute to the Aquila strings that were on it. I would have preferred some fluorocarbons. I did find the comparisons to Martin concerts a little off the mark, however. Collings concerts sound different to me - less ping, but fuller and more even. What I mean is don't buy a Collings because you want a Martin but want something new. Buy a Collings because its a great sounding, extraordinarily built instrument. I played the Collings side-by-side with an array of high-quality ukuleles. Nothing else in the store could top it, in my opinion. A Scott Wise koa concert was pretty darn good though. The clerk told me that the only instruments he thought would likely please me as much if not "Moore" were Moore Bettahs. Of course, there were none of these in stock. Boo!
I can't imagine being disappointed with a Collings (with the exception of the I-really-want-a-Martin matter). Highly recommended.