I've been having the same internal debate. On one hand, it sounds convenient though maybe a bit gimmicky. On the other hand, how often will I truly grind twice? Not to mention, the added HP (I will be grinding whole rabbits) would be nice, and should I ever decide to use a mixer, MYM's mixer only works with their 1.5hp grinder. So far, I'm leaning towards the 1.5.
Also of note, apparently the dual grind wasn't included in the recent 25% off sale they had. Not sure if it will be in the future.