Haven't used one myself but from what I hear, they are pretty good. Takes about 500 miles to completely tune but when you consider that there is no dyno runs needed for setup, the purchase price isn't so bad and the bike is spared the stress of the dyno runs. You also don't have to deal with an incompetent dyno operator that can't tune a bike properly. The wide band 02 sensors give you a pretty good map as compared to a canned map or dealer download. Many have reported that their bike has never run better.
the t-max Auto tune is what I'm going to over the winter....I've been looking at everything I can find for the '07's and newer with the oxygen sensors. I like that it uses the wide band sensors and thats why I decided to go with it. Terry Components make a plug and play auto tuner called the Terminal Velocity II that runs off the stock sensors for about half the price, but I've heard a lot of mixed reviews about that one. from what I can figure from everything I've hear and read is that the TV II is a close second the TM Auto tuner if you run close to stock motor. most of the people running high compression-big bore-cammed up engine didn't have anything good to say about the TV II, and would go with the Thundermax. I wish I had it on right now so I could tell from actual experience, but when I get it on there I'll let ya know.
As long as you stay with common bolt on upgrades, (intake, pipe, cams, under 10.5/1 CR) it will run as good and make as much power as any Dyno tuned engine. If your going to be making multiple changes over time the Dyno time alone will cost more then the Thunder Max. :53: