What coins actually you want to mine maybe I can give you some idea if what wallet would be the best, And could you tell us if what are available devices of your friend?
I might just tell him to get Coinomi beta setup on his iphone. It's the best solution anyway.
Cheers
Just in case you want to pursue nicehash, then I guess what you need to worry is the history of its security breach, and also its TOS citing that they are not already liable on any future hacks
The good thing is you can freely transfer your BTC funds to Coinbase free of charge.
Yep, it would work, been done that when I need a fund to simulate NH's cloud mining, pointing out some of my rigs from MPH pool