They've been around for a while (years). Their AR15 gas piston upper product is actually old news now.
I've had a couple of opportunities to shoot their 5.56 AR product. They appear to be of very high quality and reliabilty. A bit heavy like many gas piston uppers. They shot well. I've never heard anything bad about them other than they are somewhat expensive and delivery times can be a little long.
Both weapons I shot had side-folding stocks, which in my mind is the only reason to get one. That feature is incredibly cool and convenient. I still don't get the whole reason for gas piston AR systems other than that, though. Sure, they stay cleaner, but my AR will run for at least 600 rounds from a clean condition and has many times and I didn't think the felt recoil of the ZM was really any different, either.
Anyways, if you've got your heart set on a 5.56 AR gas piston set-up you might also look at the POF and LW gas piston uppers as well. And you can always get one of the ZM side-folding stocks to go with any of those uppers.
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Edited to add: if you don't want to wait for the .308, why not just get a FAL Para?