I actually took a day long class sponsored by Westspur on SRT; ended up buying a set up that included the rope wrench, a small pulley, prusic loop, and a small ascender that strapped to your boot. The pulley kept the rope wrench traveling along with you.
One caution was that the rope wrench should not be used alone as a belay device. I ended up not using the system -- can't find the mini jumar type ascender for my boot, and my climber borrowed the pulley and prusic for his set-up. My rope wrench, meanwhile, sits pristine on a shelf, and I usually climb a static line tied to the base of the tree with my old two-jumar on webbing set up.
The whole point with the SRT set up with the rope wrench is to do small jobs while working off of one rope, to save time and hassle rigging multiple ropes, and because of the ease of going up AND down on the same rope that is tied to the base of the tree andlooped over some limbs in the crown.
Just couldn't break old habits: I either climb a static line (rigged with a throw-ball) and then climb off of a second line with a Blake's hitch, or walk up the tree on my working line (tied in with a Blake's) with a flip line around the trunk. Of course, the latter works best in dry weather!