This seems like a silly issue. VMG is nice, particularly on a super long course where you may not see the top mark, but really this requires you sailing the course and grabbing those mark points. In my experience, you don't have time in a bouy race to worry about GPS data if the breeze is up.

My point being, I have GPS equipment for distance racing that would work fine for around the buoys. I don't own a $400 TackTick. Should I? Yes, but since that is the only non-GPS enabled device on the market that gives you heading, is this really a fair rule? IMO, no, it is simply forcing people to buy one manufacturers product...