I have a brake controller on my truck. I don't like to use any large trailer without brakes...even if it is not required. Even my single-axle, 1,200 lb, 3,000 GVWR cargo trailer has been fitted with brakes. Some states require them for trailers as small as 1,000 lb GVWR, anyway. I don't like hauling any trailer that weighs much more than the tow vehicle. In difficult situations, a heavy trailer can start to push the tow vehicle around, and that can cause problems. No matter what the rating, I try to stick with no more than about 2/3 of the tow rating, or better yet no more than the tow vehicle weight. That is my personal limit, not a rule or law. Besides, towing a heavy trailer is hard on machinery. Others can do as they please, it's just my preference to avoid those possibilities.