My "Other" vote would be to look at:
IK Multimedia - iRig HD 2
I have to assume the "HD 2" makes it better than the original one, which I still have and use. The software (Amplitube) has the ability to speed up and slow down the play-along track with no tone shift, and it also has a drum machine.
I use the IRig and have now for about 3 years, I have the first generation. The app is good, has some options for amps/effects, a decent digital tuner and all music in your phone is available to play along with. The slow down function is really very good. And it is inexpensive and super small, fits in my briefcase.