I have been using a 72" First Choice/Midwest box blade for about 2 years now. It's a good sturdy unit that has no trouble with roots, rocks or anything else I have encountered. I would consider it a medium-duty implement. All the 3 pt structure is solid and not susceptible to bending under reasonable use... quite a step up from some of the low-end units out there. The biggest issue is lack of weight... it's probably only 5-600 lbs, vs. 1,000 or so for the real heavy-duty units. I strap on a few sacks of concrete, but that's not a good solution and sometime I'll rig up a better set of additional weights. Even so, it works fine in soil and gravel. If I were using it commercially, the HD type would be better, but this has my needs covered.
Incidentally, I think First Choice and Midwest are no longer associated, but Midwest is selling on their own plus some private branding.