I used to use the RR double slipper for the MGT (MOD1) with the steel spur with a homemade sprong. I didn't have any problems using it with the RR hardened steel pinions. It just sounded like a jet turbine spooling up. The sprong kept even pressure on the spur. I now use a Strobe slipper with a plastic spur, and my homemade sprong, keeps straight without wobble. I have another plastic and a metal spur spare, but haven't needed it yet.

There is a tute somewhere about putting a sprong together, it requires a thick rubber grommet/washer thing for fixing taps, a 4mm nut or bearing to put in the middle of washer to slide onto the shaft, and then a stock plate to hold everything down. Don't have any pictures atm, as I am out of the country for another few days, will post pictures when I can.