After a bit of research, I have the impression that the EMG data, which is supposed to be the special thing about it (aside from that, it's just an accelerometer and a gyroscope, which your phone already has) isn't really that useful. It has only five factory-recognized hand gestures, and from what I've seen online, there aren't loads of other ones that are easy to teach it.
From myo's developer blog:
Working with EMG signals is hard. Building an application that works for you and your friends is pretty straightforward, but building something that will work for everyone is another question entirely. The signals that are produced when different people make similar gestures can be wildly different. Different amounts of hair, fatty tissue, and sweat can impact what the signals look like, and this is compounded by the fact that the Myo armband can be worn on either arm and in any orientation. It’s incredibly difficult to transform a person’s hand into a controller, and we need to make sure that the applications in the Myo Market yield great experiences for users.
I found someone online using ML to teach the myo additional hand gestures, and they successfully added three. So for eight hand gestures total, not sure if it's worth it. At any rate, I'll be interested in hearing about your experiences.....
\M