VERY happy with my 527M carbine in 7.62x39mm. Incredible light rifle. The iron sights aren't adjustable, rugged as all get out, but non adjustable, so I found a fantastic local gunsmith who made one for me.
There IS an alternative to the proprietary rings, just most people don't know about it.
Look carefully - there is a Picatinny rail attachment on the rifle, sold by CZ-USA. Mount whatever you want.
Mine is off getting a truly custom stock put on it, one of a kind. It really IS everything everyone says it is.