Leopold's keycap sets should come with two 6.25u space bars: one that fits almost every 6.25 space key out there, and one that fits some older Leopold models specifically.
The keys are thick and I have heard about people having problems with fitting other thick key sets on keyboards with Costar-style stabilisers (that WASD Keyboards is using). I have not tested, but Leopold's space bar is thinner right in the places where the kinks should be in the stabilisers - so I think it is probable that those fitting issues would be averted.
I have a blank set on one of my keyboards (a Ducky with Cherry-style stabilisers), and it is the nicest blank set I have seen. Thick PBT, Cherry profile, very crisp edges and texture on top.
Edit: I suspect that Geekkeys' set is made by Gateron (from the shape of the F and J keys) - I have a couple of sets of Gateron keycaps and those have only slightly coarser texture and are less crisp than the Leopold's. The space bars are also not thinner in places, like Leopold's, so there is a higher risk of not fitting.