Easy to use, yes. Plug it in, tell it to load the tune. ~60 seconds later you are done.
Use it on more than one car? no, it downloads your stock tune and locks itself to your car. The only way to use it on another car is to restore your car to stock at which point it will unlock itself.
Now, you can use it on any ODBII car to read error codes...but not to tune.
Also, if you are not familiar with how to tune cars and what various settings mean, it would be best to have a tuner (like our very own sponsor VMP Tuning) give you the tune to load so you don't break things.
