From what I've read, the UTH on the totes is fine as long as it's checked on. Most of the plastic totes have a heat capacity of 110-120 degrees, depending on the brand. So keeping your dubias at around 85-92 degrees shouldn't be a problem. In fact, I just started my own colony and I'm going to be using UTH's. Just to be safe though, I'll use them in conjunction with a auto-off thermostat I have that maintains the heat at a set temperature.
In addition, human heating pads can work but someone I know brought up a good point - most aren't made to run 24/7, for a reason. It's hard to find a model nowadays that doesnt have an auto-off feature because they're known to melt things around them/themselves, and start fires. They're made with cheap materials, so I would feel safer with a UTH- because they're made and tested to run 24/7. It's all personal preference though.
Just remember if you do decide on a human heating pad, get one without the auto-off feature! Don't want your dubias to freeze! :wink: