They have glue on one side of them
The ones I bought had no glue and neither did the ones they replaced. IIRC, they used to get glued at the factory for ease of assembly but they stopped doing it to make them easier to replace.
There does seem to be a inside and an outside to them tho because I initially had some really bad slipping and it was solved by flipping them over.
In my experience the plastic spur is plenty strong for blx power given your mesh and slipper are both adjusted correctly. Another thing to watch for back there is that both the motor and the tranny stay securely fastened to the motor plate. I have had issues with both of those coming loose with use which allows the mesh to fall out of adjustment.