I don't want to limit spinning weapons because it just puts people off.
This is the opposite to how I'd feel.

Also MDF is a silly material to use for anything structural- were you to mount a spinning disc on a bulky plywood frame, perhaps with a couple of metal braces as your concept rules appear to allow, then you could get away with weapons nigh-on as powerful as your standard featherweight, not really in the spirit of a budget knock-around class.

wood working tools such as saws etc and for those to be limited to their design rpm
This however does seem a bit of a restriction. I reckon the middle ground of only permitting low-powered spinners (determined by rpm & mass), irrespective of what they're spinning is a fair compromise