I recently bought an older style injector from the 40's off ebay. My experience is that while shaving it feels quite mild, but afterward you can tell its a bit agressive. The skin can be a bit tingly, but no real irritation or redness. I get great shaves from it and would guess its no more agressive than your GEM. I have been using Shick blades that I got at the store, and they shave fine. I have only used this injector so I can't comment on other versions, but I highly recommend giving it a try.
" I'm fuzzy on the whole good/bad thing. What do you mean "bad"?"