Two amps are best (a bit inconvenient), but if you have an effects loop they're also OK. I like using it better than a metronome.I've had a new Trio sitting in it's box in the drawer of my desk for 4 years or so, maybe longer. It's the original, not the Trio+ with the looper. Until I saw this I forgot I even had it.
I tried it when I first got it and it seemed like you needed 2 amps for it to work well which I didn't want to bother with so in the drawer it went and has been there since. I have have a bunch of stuff like that I should sell someday.