i only use the felt ones.
the way i look at it if you use the solid ones you have the leg pressing on a solid spacer which presses on the decals. all you are doing is making the point where edge of the legs press on the cabinet.

but with the felt ones you have something that absorbs the pressure from the edge of the legs and distributes it evenly.

just like when you fasten glass doors onto a cabinet, you use a nylon or rubber washer under the screw head or nut where it comes in contact with the glass not a solid washer.

that's my opinion any way.