If you need the tuner to adjust your speedo for gears or shut off your rear O2's, then get it. If not, the gains are not very big and I would look into other options. If you haven't done gears, you will get the most SOTP feel out of them, only problem is you will need the tuner to correct your speedo after changing that, or you can go with a Speedcal as a cheaper fix.
As far as tuners go, SCT seems to be the best of the best, atleast when it comes to custom tunes, but Diablosport is not far behind. I have no complaints with the Predator and it is very easy to use, but again, the performance gains are minimal.