I have been using one for a while now and really really like it. The sub synth really makes my small 12 inch sub shine - haven't tried it with my 15's but I imagine it will be smokin'. The EQ curves are varied enough that you can really get your sound shaped nicely in a pinch when things seem flat. Got mine when it was quite new and pricier but no regrets! It has replaced my Behringer DEQ2496 which is way more powerful but you need a PHD in Physics to really get it to work properly...
You can sorta see how I have the Go Rack patched into my system in my Giglog from this past weekend (advance to 2 minutes 54 seconds-ish to see):
You can sorta see how I have the Go Rack patched into my system in my Giglog from this past weekend (advance to 2 minutes 54 seconds-ish to see):