Mine is an old Ciener, but the CMMG units get very good reviews. The Ciener is prone to breaking firing pins if you dry fire it much, and since it doesn't have a last round bolt hold-open, you can find yourself dry firing it unintentionally at the end of a magazine. I'm on my third firing pin at least, maybe fourth, in probably 18-20 years of use.
I rarely use the Ciener kit anymore, using dedicated rimfire uppers instead. One handy thing to know is that the Black Dog magazines work with the Ciener as well as with the rimfire uppers. IIRC, the S&W upper is different; not sure about that.
One great accessory if you swap uppers around at all is a $3.50 'bolt saver'. They keep the BCG in place when the upper is off the lower, and are worth much more than they cost. Not my pic, just one I found on the net:
Fwiw, I've bought most of my Black Dog magazines from vendors other than Black Dog direct. Other places like Joe Bob Outfitters, Midway & others are usually cheaper than ordering from Black Dog's website, especially the 50-round drums.
The chamber adapter part of the CMMG unit is prone to cracking at the very end; the part that looks like a case mouth and splits like a split case neck.
When that happened to mine I did what I was contemplating anyway and assembled a dedicated unit and a buddy of mine machined the chamber piece to an exact copy of the dedicated upper adapter CMMG sells.
Of course CMMG will automatically replace any broken piece. I was talking to a young man at the Crowder Range who had the same issue.
I bought a Tactical Solutions dedicated .22 upper about 14-15 years ago, it ran great until the springs weakened after about 5,000 rds and I couldn't get replacements. Then I bought a CMMG (Echo) kit, fantastic system, never had a problem since. I run both with Black Dog magazines.