Sorry to bump an old thread, but this is relevant:
Packt Publishing now has a subscription plan which seems like a great bargain: $9.99/month or $99.99/year. I went for the annual plan.
Their video courses are also included. Of course the library extends well beyond Unity and Unreal, so could also be helpful for C#, C++ and points beyond.
They have apps for iOS and Android, and I can report that the format on Android looks good.
https://subscribe.packtpub.com/
