Yep, the HN Isolator is one I'm constantly pointing people toward...especially if they intend to do any live work with their modular. In your own studio, you've got all the time in the world to chase down ground loops, noise, etc etc...but when you're on a gig, you don't have those luxuries. By relying on the transformer isolation in that, a HUGE percentage of the typical electronic crud issues get cancelled, and you don't waste time futzing around with trying to figure out where that annoying hum, etc is coming from. $100-ish for sonic peace of mind is well worth it!
Also, you can push the transformers a little bit and, like all BIG IRON in the audio path, you'll get a bit of a warm-up to fill out your signal. And, as noted, the venue will be very happy that you didn't pump some DC into their expensive-as-hell sound system!
the-erc: You should check out the Isolator's big bro, the OUT. Stereo ganged level over both the incoming main stereo signal AND a parallel stereo-in, which just begs for use as an extra FX return...with panning! Stereo metering, headphone preamp, more IRON and balanced TRS 1/4" outs. Actually, the ganged stereo controls make a lot of sense from a mixing standpoint; they're equivalent to your desk's Master fader, which also (usually) functions as a stereo control.