i have a large farm in s/w NH - believe me, i feel your pain..
a large scale logging operation left (in addition to trashing the interior trail system) HUGE slash piles; an extensive interior trail network was littered with stumps, etc.
i burned what i could push into a pile (mostly in fields, for interior trails i did my best to create large piles by hand or with the tractor); some of my burn piles burned for over a week.
the brush grinder you reference is a good machine; i've seen them in action. they are fast, and with an experienced operator, might make perfect sense for $1,000/day.
if it were me, i'd burn what i could easily pile. for my interior trails, i use my tractor (w/BH) to remove stumps that are in the way. in areas where my tractor can't go, i use a utility ATV to drag/push brush to the sides of the trails.
the critters (and the forest floor) don't mind the extra slash.. and as long as i can drive a snowmobile/atv through, i'm happy..
if you have more specific questions, send a PM and i'll be happy to help out anyway i can..
good luck.
pf