My 455's have quite a few rounds though them, and they cycle very smoothly. I would say that after 1,000 rounds or so through them, they were both free of any dragging or burrs.
The safety is stiff, but I don't use the safety too much. The CZ safety is a bit contrary to my upbringing, so I usually just carry them unchambered, and chamber when I'm about to go work. That's a long explanation as to why my safeties haven't really smoothed in a comparable way to my bolts.
I have a almost NIB 452 .17HM2 I just got, and it is much tighter, and not as smooth as my 455's - it has an extra lug, and more bearing surface. I'm sure it will smooth out once I put the 2,500 rds through it I intend to this spring.