I'm building a SAB too. I have no idea what I like working in yet honestly. Gonna try both soon.
Also keeping my eye out for good parts I could make a nice LFH\full work bench from in the future. I have corian sheets picked out allready for the countertop bench, with enough for full back splash up the wall, for easy clean area.
I've seen a few people use them hooked to totes, but I believe having the bag actually creates some kind of true laminar flow, due to the fact the bag is constantly changing in shape along with the flow. Like, it absorbs any turbulent eddies that would otherwise be created in a solid box. Then again, some guys apparently had good luck with that, and even reused the arm hole cutouts like flappers.
I think the bag is the safest bet, the way it handles the flow. I'll try with a tote too maybe.
I wish someone would test one, with a fancy air quality meter. Find out what variations work best.