Back when I first started, I lost a tiny King hatchling that escaped out of a shoe box tub. I've tried them again on occasion with other animals, but personally, I just never trust the flexibility of plastic tubs. They obviously work better with a rack ceiling, but if you are just using the tub and it's latching top, there aren't a lot of good ways to conveniently secure that top - at least to my satisfaction.
I worry less with a glass tank. Glass tanks come as small as 5-gal, which completely covered and insulated, is working well for my BP hatchling. He has eaten twice for me, no problems.