The Cobb Accessport is a great handheld tuning device. Cobb has done a great job making these devices for some of the most popular turbocharged cars to date, including: BMW, Ford, Mazda, Mitsubishi, Nissan, and of course, Subaru. When you buy an Accessport, Cobb will have already pre-installed some tunes that will make your car crank out more power; they have been thoroughly tested, so you don't need to worrying too much about your car breaking down. However, Cobb does have a disclaimer warning the user that they hold no responsibility in any damages, should you risk installing their tunes.
I have personally been using the Cobb Accessport ever since I bought the car, and it has been a great device. The Cobb Accessport even allows drivers to set things such as launch control, and flat foot shifting. I have been using the launch control feature a lot during autocross events because it gives me a consistent launch every time.
The Cobb Accessport v2 is a smaller device, but ultimately does the same things as the newer v3. The only difference is that the v3 has a larger full colored screen, so displaying real time data is much clearer and nicer to look at. There is also a nice new feature on the v3 that the v2 didn't have, an off button. That's right! I find this function very nice, especially if you plan on never removing the Cobb Accessport off its mount. In the previous version, you had to unplug the OBDII cable from the device every time you wanted to turn off the device. Even removing the key from the ignition will keep the device turned on. However, in this newer version, there is an off button on the top of the Cobb Accessport. It will prompt a message when you hit the button saying something like, "The device will turn off in 10 seconds. Hit any button to cancel."
If you leave it, it will shut down even with the cable plugged in. I found this feature as a major bonus on this new device. A small edition, but an important function in my honest opinion.
Pros and cons? Well, it is a much nicer device compared to the v2, but you'd be paying around $100 more for the v3 just for the bigger screen and the off button. The tunes are identical, so you will not be gaining more performance from this new device! If you are a person who just wants to load the Cobb tunes into your car and never plug your device in, I'd say stick with the v2. If you are someone who wants to have some nicer looking gauges, or if you just like having the latest new toy, then I'd say you'll love the Cobb Accessport v3.