I had a SIG Pe90 and while it is a good gun, it is too heavy for it`s caliber, the ergonomics are not as good as the AR (for me), the mags are expensive if you can find them, accessories are scarce and expensive (how many of you got airsoft cheeks rest?!?)... Plus, the accuracy was not much better than any run-of-the-mill AR. It was unrestricted, that`s a good point! I sold mine and did not regret it (much!)
I`ve been waiting for the XCR for over 2 years now... On paper, it is better than an AR while retaining the ergonomics, it is unrestricted and light. Once the folder is fixed, it will be handy to carry around as well... I believe it will be a better rifle than either the AR or the SIG PE90. As far as spare parts go, of course the AR is impossible to beat but SIG parts do not grow on trees either!