I don't know if my CMMG conversion is a Ciener, but it works crappy with bulk box Remington ammo. A bit better with Federal and flawlessly with mini-mags. Dollar wise, I wish it was the other way around.
My middle son has the GSG-5 and it's OK. I like my conversion because I run an M4-2000 on the end and it's really quiet that way.