Re: rack gear?
Make sure you can return it! Not that it's a bad idea or unit, but there are potential problems:
1) These things lock in on feedback frequencies as they start to occur. With mics, there are a couple frequencies that stand out, depending on mic & monitor combination that's feeding back. Guitars have a BUNCH of different frequencies, depending on what you're playing (unless a microphonic pickup is the problem). You'll be locking down a lot of frequencies over a set.
2) Because it uses narrow band filters, you'll change your sound. For this reason, only use it in the monitor loop. If your feedback is coming from your amp or your mains, this won't help and you'll have to put this unit in the FOH (main) signal chain. Not good, sound-wise.
3) By cutting hum this way, you'll cut 60 Hz on your guitar, and probably some harmonics (120, 180, 240, etc). This will suck out your bass (especially if you use a 7 string or detune to B)
So, I would try to fix your problems at the source. For hum, look over your amp and pickups to determine if there's another fix you can live with. I can almost guarantee the result will be better than filtering after the fact. For feedback, figure out the main causes and fix it there. Feedback destroyers are band aids.