Doug,

The H21SC has a shorter mast and smaller mainsail then the racing version (SE). I think it is not a safety requirement to have mast rotation control with this rig, but depending on the shape of your mainsail, it could help trim the sail better. But why would you worry about this kind of detail in a cruising boat? Just have fun!

If you want to add something usefull and improve safety, a righting pole would be the first choice in the 21.

Cheers