when used hp tuners come up for sale, sometimes they don't have any credits left, and those ones aren't worth buying because you only save 100-150 bucks. a new one will run 500 for the standard or 680 for a pro. the only real difference is that the pro has an input that you can use to get data from sensors not part of the engines obd2 system, like a wideband. they both come with 8 credits, so you could tune 4 cars without buying more credits. the hp tuner is easier to learn, set up and use. I started with a dhp, then sold it and bought an hp tuner. the hp tuner has some features the dhp doesn't have, like when you make a mass air flow sensor calibration and your fuel trims need to relearn, when the hp tuner is used, the relearn is rapid, like within a few minutes. with the dhp, it can take up to an hour of driving.