Back in about 1983 I ordered in two ZKK602 Brno's, a 375H+H and .458WM. Recall shop got me them for $475 each approx. The .375 functioned ok out of the box but required hours of cycling the bolt with bore scrubber to smooth out. The .458 was so rough it could not chamber a round. Working the ramp eventually helped but it was always a rough SOB. Dumped them both within a couple years. Typical commie "cold war" quality IMHO.
Havent handled a 550 but I've heard good reviews and they sure look nice in pics. I suspect the earlier pre-1980's ZKK' Brno's were a little better finished. The Brno's of the 50's are second to none, just lovely, I have two 7X57's.
My opinion of course.