I'm no fan of John Ciener from all I've heard of him and an effort at communication with his company.
I've got AR conversions from Ciener and CMMG to Spikes, M261, Air Force, DPMS, Colt, original Atchisson. 1911 conversions from Colt, Advantage Arms, Tactical Solutions and a mystery one (Colt markings but Pachmyr design).
The only ones that are breaking are the CMMG SS LH units - poorly welded backing plates.
What we should remember is Ciener popularized the .22 conversion for a wide variety of firearms.
ARs, Mini14s, 1911s, BHPs, Glocks, etc.
His stuff worked and in the ARs could, with the FA parts, run full auto which none of the other conversions (Colt, M261, Air Force) could. The original Atchisson, which Ciener modified, was supposedly made in a FA version but I've never seen one or heard if they worked well or not. I have a original SA Atchisson and have never been able get it to even fit in any of my uppers.
That said - I think the best game in town is the current CMMG units. They've done the most work on the conversions of late.
YMMV