Does the 1/2 speed and reverse effect also work with backing tracks or only with the recorded current loop?
Yes it works. Once the loop is imported from your computer to Ditto X2, you can apply the 1/2 speed and the reverse. Be aware that your own recorded loops will be also affected by these settings. Furthermore, you can select one function, the other or both functions for the backing track. These options are available also for recording and playing you own loops as well.
For further information on this topic, please see this additional FAQ: Ditto x 2 Double time & reverse