Excluding SE is to make sure people do not spam customer support and launch annoying phishing campaigns. None of that is applicable for local software running on your own computer.
Quick googling gave that Stockholm is deeper on average, although the deepest point of London metro is currently deeper than Stockholm. No drastical differences that should affect this question I think.
(This will change when they are done with Sofia station, a new station in Stockholm that they are building 100 m below the surface.)
Edit, forget what I said. I missed the keyword 'paid'.
Threads earlier this year apparently got 70 million user signed up the first 48h. I would assume this leads to at least >1m Android users?
First example I came to think about, might be much better examples out there. Regardless, something with "more than 100,000 people" in 48h is probably not the fastest growing Android app.