Some dont fit right, others are a perfect fit
They are not very precise so some will fit perfectly others may be too small and useless. Combined with non precise wheel cores, it's hard to get all four to work. If you get lucky then they work great, however warp eventually (depending on riding style). If you demand precision and durability get some Logic spacers from PL (not too expensive either).
I don't know why, but I can't crank down on these quite as much as on my other set of bearing spacers, which are generic. When I crank down on the axel nut, the spin is better than with no bearing spacers, but not as good as if I back off a bit
These are good, but they warp under intense riding. Made of aluminum and not steel. Don't use these if you are going to be riding a lot.