Bitcoin is a digital asset that can be used to store and transmit value.  I think your friend should pray about it and listen to his conscience.  As a Christian, I have no concerns about bitcoin as long as I am not turning into an idol.  That would be my greater concern, but that is not limited to bitcoin.  Anything that replaces Christ in our hearts is a danger to our souls.   Hope that perspective helps. 

 Very helpful! Thank you!