Yeah, I had a K1 and a K2 way back when, and wish I had never sold the K2 (which I believe is the same as the AR100? - AK style piston and side folding stock? The K1 had a DI system like an AR15, and a telescoping M3 Greasegun-like stock...it worked but...).
For those that are having trouble understanding the excellence, let's see if I can help. The lower was very similar to an AR15 internally. The upper had a gas system that externally resembled a FAL, with a full length piston like an AK, and a rotating bolt like an AR. It had excellent ergonomics (as good or better than the AR in my opinion), and a nice trigger.
Downsides, by todays standards, were a pencil barrel, no rails, reciprocating charging handle (back then, that was considered a plus!) and it required an adapter to mount a scope out of line with the iron sights.
I'd love to have another, but considering I bought mine new for about $300, I don't think I'd ever pay $1200 for one.