Active users is the standard metric used to check how much a service is used (at least as far as i know. its what i see when i look at stuff published for investors).
hexbar is on the sixth place in term of number of active users with 1.8K , lemmy.world is 18K (enable the "active users" column and sort by it to see the full list)
gocryptfs is very fast for me. i have a file with about 5600 lines and i detect no difference when opening it under encryption and not under encryption. but in gocryptfs each file is encrypted separately . so you could get some information about the directory structure. but the name of the files and folders is encrypted ("archive" for example turns into something like "AaL6P86WWMnqQkMYnsRBXg").