I agree that any instrument that requires a computer to properly program is as good as a softsynth with a hardware dongle. I don't need to boot a pc and enter a password to play a guitar, I don't want to do that to use a synth either. I'm not so worried about needing a computer to program a controller, but that's not playing music, that's programming a device. [/rant]
I'm using a Bitstream 3x to control my Tetra. It doesn't do 14bit MIDI so I've spread a few of parameters over two faders. At first I thought it was going to be a pain, but it works better in some cases to have a separate controller for the upper and lower ends of the parameter data. Originally I was using a Remote Zero as it has eight 14bit capable encoders but didn't like having to change templates all the time due to it's limited number of controls. 24 vs 40 makes a big difference to logically assigning which parameters to which controllers. Having LFO speed next to Cutoff because I need to put all the 14bit parameters next to each other doesn't lend to intuitive tweaking really.
I've just bought a BCR-2000 and thought about programming it to control the Tetra, but I've waiting for one at a good price since I read about Zaquencer and don't want to waste time programming another controller for a box I've already got covered, not to mention I really don't want to think about Tetra NRPN's again for awhile, heheh.
But that said, I've looked at it's programming software and it seems logical enough and actually a bit more sophisticated than that for the Bitstream and the Novation (which is actually a beta and not available from their regular downloads repository). If this is your first time programming NRPN's it might be a bit daunting, but it's not hard to learn how it all works and then work out how the controller company has implemented the programming of NRPN data.
tl;dr
Yeah, get a controller and keep the Tetra. It's a very nice machine. The Prophet will take up too much space.