My experience with it would say it's a smooth system. I got the UCR model and think it's pretty nice. The reason I will talk "bad" about it is because I don't think it's worth the price. All I got was the Dead Air brake and ALG trigger and it cost a lot. I don't feel I got what I paid for. Plus they put what's probably the cheapest and crappiest stock on it I've ever seen or felt. Ships with a whopping one magazine. The operation is nice and so is the trigger. Fit and finish seems to be nice to me too. Ships with a whopping one magazine.
I have the Meridian, a ZPAP and a preban Hungarian SA-85M. I don't feel the Meridian offers me anything the other two don't besides the nicer trigger. It almost feels the same as my SA-85M. How it compares to something else like the Pestilence or the Volk model, I'm not sure and can't speak on that.
Fit and function seem great and I'm sure it's reliable as I have heard nothing bad about it. The biggest thing for me is it's not worth what I paid for it (in my opinion). Not to mention I waited about 62 weeks to get it in my hands. i originally wanted the Volk, but for the almost $3k they charge, I couldn't bring myself to spend that much on an AK.
If it was my only AK and the only one I had experience with, I'd be happier with it and I'm sure most people are. I don't mean to put you down for buying one and hope you love your purchase. I'm just sharing my experience with them because like you said, people don't really say why they don't like them, just they cost a lot and the wait is too long.
At the end of the day, to me, it wasn't worth it. In fact, I'm considering selling mine at the moment.