Why are there so many different slide stops on CZ’s website for metal 75 guns?  
Is the difference minor cosmetics (finish, size/Texture of the exposed lever, etc) or are they so different as to not be interchangeable?  

The basic CZ 75 in 9mm only has one slide stop now. The 40 cal version will be slightly different. The CZ 85 has a longer slide stop for use with a right sided (ambi) slide stop lever.

The SP-01 has a thicker frame than the regular 75 so it has a different slide stop.

The compact pistols have slightly different frame dimensions so a slightly different slide stop is required for each frame material, be it alloy or steel.

Any other changes are just cosmetic changes over the years.

Speaking of rolling changes, If you look closely, almost all of the DA/SA CZ pistols have newly shaped triggers that are much less hooked. A very nice change if you ask me.

Is the slide stop for the CZ 75 made now better than the one made in the 1990s?

No. The older slide stops were cast and the new ones are Mim. So long as casting is done correctly, it produces parts that are stronger than Mim parts.

Thanks. I guess there aren't any aftermarket ones.

IIRC, more than a few CZ 75 slide stops have gone down with only several thousand rounds through it. Maybe those were MIM.

CZ started with MIM around 2017.  That's why I avoid CZ-75s made after 2017.

The Cylinder and Slide Shop offers a tool steel sear for the CZ-75 and maybe they will produce proper slide stops.

Who makes a good cast slide stop nowadays?

Cajun Gun Works makes an aftermarket slide stop but it is shaped differently than the OEM ones.

I'd be happy to just find slide stops in stock somewhere.