Model 1 also uses the Ciener bolt without the chamber adapter; the design is just like the Spikes. I don't know about others. Model 1 also sells barrels, bolt assemblies, etc. if you should want to build your own, say if you have an upper with a shot-out 5.56 barrel you are going to replace anyway.
I have a Model 1 and I love it. Prices are good, turnaround time is good, and they have a nearly-endless variety of available configurations (bull barrel, fluted or unfluted chromoly or stainless HBAR 20", light and heavy 16", SBR's, etc.). Mine is incredibly reliable and it just keeps on shooting. Unlike a lot of .22 semiauto rifles, I don't have to clean it often to keep it feeding, although I do clean it now and then. A little bottle of CLP in the range bag in case it goes completely dry should allow you to shoot at least 4 bricks straight, no problem. I think there's just a lot more space in the receiver than a regular .22, so it takes a lot more fouling to slow it down.
However, I can't give you a comparison between Model 1, Spikes, and some of the rarer ones. I only have one .22 upper -- so far. People with the Spikes seem to love them, too.
I'm damn tempted to get another one, it's so much fun. Maybe a bull barrel or fluted HBAR with a scope or something. I shoot my 16" heavy barrel carbine at 100 yards with A2 irons, and it works great, BTW. But I could definitely get more target-shooting accuracy with a scope than with the military sights. Unfortunately, I only have so much money to spend on guns. The one-handgun-a-month law here is getting really expensive. I have a hard time affording it, but the law's the law.
Model 1 has a number of magazine options. I'd call them. Ciener makes a hi-cap and a 10-rounder, and they're VERY well made -- they're welded parkerized steel. And of course Black Dog makes a bunch, too.
http://www.model1sales.com/
There's no reason to change a trigger group or anything else. You just put the upper on a standard AR lower, stick in a mag full of .22LR, and start shooting.
