I've never heard anybody talk about them.  How's it work?

I had 2 of them. 1 would run FA in a mini 14, just pull the trigger.
Absolutely no mods to it. It ran like a sewing machine.
I sold them both. I also used the BDM skinny mags but the Ceiners ran better.

I dealer near me bought a Ciener Mini 14 kit for a customer from Brownell's and installed it in the customers Mini 14.  The dealer could not make the conversion kit work.  The magazine lips were so soft you could bend them with your fingers and the lips would bend while trying to insert the mag into the mag well.  The kit it self just seemed to off such poor quality we didn't think we could ever get it to work even with a good mag.   The dealer and I both have owned Cierner kits for AR 15 which were made to higher quality than the one Mini 14 kit.  Fortunately Brownell's took the kit back and shortly after this Brownell's quit being a dealer for Ciener.  It seems to be a crap shoot with Ciener, you may get a good one and you may not.  Ciener is noted for have very poor customer service.

Kinda funny. I had a Ceiner kit for the AR and I had numerous problems with it. Couldn't get rid of it fast enough, even with BDM mags, CRAP.
On the other hand the Mini kit ran like a champ.

Dad has one for his AC556, but we've never tried it.  If yours ran that great, we may have to give it a try.

The one I had for my mini 14 worked great.   I still have it and no mini 14.  Someone make me an offer!?

I had one and it ran great with ammo it liked.  I did not like Remington for some reason.

I have two for my AC556. First one lasted about 6 months, but was used. Second one is a newer model. several years old and still running, but doesn't work so well in cold weather.