There is 
I’ve been tracking the growth of Monzo’s users, based on users who’ve shared their user number & activation date (if anyone’s reading this who hasn’t already, please do post yours here 
), in this spreadsheet -
When it comes to active users, Monzo said that
60% of cards [are] being used actively (at least once a week)
in their investment deck for the most recent round of crowdfunding.