Depends on the phone. You need to have BLE (Bluetooth Low Energy), aka BT Smart or BT 4.0 or higher, on your phone or tablet. All the latest iPhones and iPads use that standard, but many Android phones and tablets still don't. If you handset is compatible, pairing is immediate and, in my experience anyway, rock steady. If you have an iPad you will see the most benefits from the interface and companion app, as you get lots of additional info (if you get a fault code for example, you can touch the code on the app to get a more thorough explanation of what it means in English, instead of a cryptic alphanumeric string), you can email yourself files and codes, you can see graphic representations of certain live tests, etc. The Android interface is somewhat more crude, but the app is quickly catching up with iOS at each new release version.
The BT interface could open the door for an even more sophisticated and easier to use app in the future as the guys at Gap add more features to it without the forced hardware and software limitations of the self standing module w/o Bluetooth, which is why I would recommend spending the extra money for the BT version, if you can wing it.
