Is that a genuine BMW Z3 hardtop? I ask that because those brackets (those big parts in your picture) are not original BMW. They look home made.
Proper BMW ones look like this. Note also the wire on that left hand bracket. That's for the heated rear screen.
View attachment 231563
Looking at your pics I can see that the 3 mounting holes kind of look right and the tube that the roof pins slide down into appear to line up - but the brackets, as a whole, appear to have been made by somebody. Maybe home made or some other company who're selling an alternative bracket.
I don't see any facility for heated rear screen either. Also no switch for said heated screen.
I also want to mention fore, aft, up, down adjustment (ie during first fitting). I'm sure those aftermarket ones have that capability but it looks like a bit of a fiddle. Any documentation you find that describes how to fit a hardtop will describe the original BMW adjustment so won't match those aftermarket ones.
The original kit also has plastic covers that hide the brackets when not in use. Covers are not shown on your picture and it's possible that if you found those covers elsewhere they might not fit those non-BMW brackets.
Apart from that. If they're cheap and you're happy to fiddle with the adjustment and you don't want a heated rear screen (I haven't bothered with mine) then they may be a good deal.