So the tech 2 is a godsend for diagnosis and minor changes on modern (ish) GM cars. It's not a tuner, though there are ways (I think) to flash ECUs with it. For the Saab I have another board for flashing our ECU and the tech 2 is just for diagnosis and working on modern electronics. Example, the TWICE unit in the saab failed a few years ago, and since that unit does security the car wouldn't fire up. The only way to make the car work again was to program in a new TWICE unit, which required the tech2. We were able to steal the TWICE from my sister's car, program it in, finish the race, then program that unit back into her car and get her home at the end of the weekend.
I don't know much about the HP tuner stuff at all, I don't know if it has the security features to program modern boxes in and out of the car. It very well may offer you a tuning solution if that's your only goal though.
The tech 2 is not fun to use. It's super old tech, it's slow, mine doesn't work when it's cold, but it has paid for itself already in being able to recover from failures and finish a race. I think they're worth it, but your mileage may vary.
Theoretically, if you have a computer with a PCMCIA slot you can buy 1 memory card and then flash the different software packages for different vehicles onto it as you need it, so it can be used with more cars. I haven't tested that part though since I own no other GM vehicles other than the saab.
let me know if you have any specific questions.
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