Anyone use one of those cheap unbranded Amazon tone generator / wire tracker? How bad?

I'm a field engineer and I need one for work. I keep running into situations where I need one but don't have one oh, and I was thinking about buying one of those $25 ones off Amazon and seeing if it's any good. Instead of dropping $80 on a fluke.

I'm a little worried but at the same time it only does one thing... how bad can it be?