Thanks, I’m glad you find this interesting too 
Exactly, unfortunately, I don’t think this those other numbers are available. The only other stat that I have, for future reference, is Monzo was seeing about £700k of spend per day on average, at the start of December which is obviously just under £100k of daily spend per 10k users.
So they’ve obviously come a long way, since they celebrated processing a total of £20m of spend back in August, when they had about 34k users 
But we’d need to know how that figure changes in the future / has changed, in order to draw any conclusions about useage.
I’m guessing they don’t want to either. As I’m sure you’ve seen, Fintech startups (that’re privately held companies & funded by investors) are generally pretty secretive about these kinds of figures & I wouldn’t expect Monzo to be any different unfortunately, even though they are being open with pretty much every other aspect of their business. I think that’s fair enough.
I don’t think they mind this tracking though (I did give this some thought before creating the graph though), as this single piece of information isn’t really meaningful - in theory there could be 100k users signed up & only 1 user who still uses their card…
Plus users obviously like to show that they were early adopters, by sharing their user number & the media like to quote the figure so I think Monzo will want to keep sharing it & I’m sure they considered the implications before they started sharing the figure.
As you say, I’m sure competitors have done something similar already ¯\_(ツ)_/¯ some of the media could do a better job of researching this figure before they publish it though 