I dive a transpac with a single tank for OW, and a Nomad EXP for cavern diving. The thing I really like about the transpac, is that it's 100% customizable. I've gone through several "generations" of gear set up with my transpac as my diving style has changed, which is certainly better than buying a new BC every year. If I was going to buy a new sidemount system, I'd probably go with the JT.
That said, if it doesn't work for you, then it's useless. Have you tried out the Hollis SMS? I know several people (even transpac divers) who preferred the Hollis over the Dive Rite, and Hollis gear is generally made a little better, and holds up a little better to abuse.
In either case, you'll be spending a pretty long time customizing everything so that it works the way you want it. If I had it to do all over again, I might just fork over the $200-$300 for a sidemount course.