The only advice I can give you is this:
1) if the Pre B CZ75 you buy is early enough/old enough you'll have a hard time finding parts for the safety if you ever break/lose a part
2) if the Pre B CZ75 you buy is early enough/old enough the front sight is staked in, sort of like a 1911, and finding a replacement and getting someone to install it is pretty tough.
3) same goes for the barrel bushing.
4) for some you'll have to either buy "Pre B" magazines at $10 or $15 more per mag. or modify/have modified the interior of the magazine well/frame to allow the use of newer magazines.
If you find/buy a CZ85 Pre B then 2), 3), and 4) still apply as well as:
1) the right side of the frame would have to me slightly modified (hole diameter enlarged) if you had to replace the right side slide release.
People get around the above (if needed due to wear/tear/damage or just inclined to upgrade their pistol) by finding a shop willing to modify the slide to allow use of newer style front sights/barrel bushing and enlarging the right side slide stop hole if it's a Pre CZ85.
If you like working on an old gun, or paying to have it worked on then it won't be an issue. I bought a Pre CZ85 a couple years ago and it was fun (stripping it down, cleaning it, buying/replacing some of the parts myself and sending it off to be refinished. It's a sweet looking pistol now. But I would not do it again. Some folks here have done it several times. It's like a hobby for them. Depends on your personality and your wallet.
Sorry, just realized your post is in the Compact section, so Pre B's shouldn't be an issue. You should be able to get parts for the Compacts (I don't know of any Pre B Compacts or CZ85 Compacts) to repair or upgrade them with no issues.