I really like them. They are available in several different configurations to make it easy to mount the instruments. They are all aluminum and use 6-32 threaded inserts. The full "circle" units are quite stiff, the split ones are somewhat flimsy and require a bit of care when inserting the mounting screws so the captured nuts do not push away when the screws are inserted.
An aid to help align and capture these rings is to use a length of 6-32 threaded rod. This gets screwed into the ring in one of the mounting holes and helps to hold, position, and align the ring with the instrument and the panel mounting hole. The remaining holes get their screws inserted, and then the threaded rod is removed and then that position gets its screw.
I use them in both of my airplanes.