In this case, user manager is not something you need to use!
use traffic flow, graphs, snmp or any other method but not usermanager.
Me perhaps, but how do I give users their own individualised access to only their own data, in a format they can comprehend and for a specific billing period?
Presently I'm generating a report in User-Manager (or trying to - the report generator doesn't seem to be totally reliable) cutting and pasting it to a text file and importing that into an Excel template which automatically combines rx and tx into a total traffic figure, compares that to the user's monthly allowance and generates a % result so that I can tell the user 'hey, you're only 10 days into the month but you've already used 50% of your allowance," because that's what they want to know - and really all they want to know so they can fine-tune their usage and choose whether or not to run up excess MBs at the end of the month.
It works, and doesn't take too long but it's still a daily chore I could do without.