I had a Loos PT-3 gauge for a few years and sold it a few months ago on ebay for $93 + shipping
. My personal experience was that for tuning only one rig (mine) it was useful about half a dozen times to get a feel for the proper wire tension, and after that it was just taking up locker space. YMMV. I also found that much less than the recommended tension was ideal to keep the drop boards in my sole from getting stuck (I do have a wooden boat, though.) Now, I just tension the rig enough so that the leeward side isn't slack when going to windward and the mast
stays nice and straight in column on either tack. My advice would be to find one you can borrow now and then and see if you really want it in the long run. Save some boat bucks.