I'm not 100 % sure if this holds true for Pixies, but I suspect it is true of all burrowing frogs: Frogs usually burrow to avoid heat, so when they dig down they can burn themselves and/or dry out.(I'd love if someone would fact check me on this and confirm/correct me.). The other issue is that on most heat pads on the packaging there is a warning to only use with Glass tanks, with the exception of Hermit Crab Heaters. This is one detractor to sterilite bins and plastic tanks. I like them because the 90 qt is roughly 20g and has lot of floor space rather than focusing on vertical space, so a land dwelling frog has plenty of room. I recently was informed they they eventually cloud over and lose visibility, and I've heard glass holds heat better. When winter rolls around I'm going to be getting an 11$ heat lamp with a 50w Red Heat Bulb for my pixie, or a ceramic heat emmiter.
Also, just a matter of preference, but Pixies spend a lot if time burrowed. Mine barely does anything all day, whereas my Toads are pretty active. I often look up to see them staring at me or hopping around. I find toads are a bit more engaging, but both are fun pets. I haven't kept a Cane toad, though. I hope this helps!