Matt,
Just for what it's worth, I remember reading the manual (yeah, I'm one of those) that came with my JJP-12. On the spec. sheet, the only difference on the HH, other than the head, was the feed rate. The straight knife one is 20 FPM and the HH was less. I seem to recall there was a difference in the motor as well. Unfortunately, the manual is out in the shop, about 100 feet away and under about 2 feet of blowing snow, so I can't quote exact.
When I read that, I thought changing to a HH head might be a bit more involved than I thought or that I want to do.
I would say that if you really need the HH, then paying for it now (only hurts real bad once) might be a better option.
Greg A.
Some people seem brighter after being set on fire