Welcome back there Matt,
Personally, I'd never use one of them plug-in testers.
If they were as good as they said they were, everyone would be using them and we wouldn't need test equipment like meters and the like.

I've had a pair of these for the last 20 years, pretty much you can test anything AC or DC from 120V up to 750V safely.

[Linked Image from electrical-photos.com]

{Sorry that is a shocker of a pic}

It has an internal solenoid (by pressing the black button)and will draw about 240mA, so there is no getting any "ghost voltages" mucking up your readings.

One other thing about them is, they are made to last, they are sealed against moisture and when the cord between the probes are un-wound, they can be draped over your shoulders (around your neck), so you know where they are.
In umm, hindsight, it does not pay to sit on one of these testers, them probes are very sharp, as I learned once. mad grin