I haven't used Zilla UTH so I don't know how many watts they run (or how hot they get?), but it sounds like they are trying to protect themselves from anyone melting
their plastic tubs & trying to sue? If you are using it with a quality functioning thermostat (as you should be), I suspect you're ok...what is the hottest that it gets?
And are you ever running it full blast? (like in a really cold room...?) Personally, I'm a glass tank user myself, hopefully others can chime in on this? Used with
higher temperatures, plastic cages of all kinds can melt or warp.