"Research produced by the University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin"
Can you please share the reference of this research? This is really an interesting fact, would definitely like to read more on that research.
Do they have stats of other cryptos too?
I think if we have to take a guess, Eth wallet will be the second most used in the world.