I think the more important thing as far as you are concerned dude is that you don't need to worry about your total usage per se. Virgin Media don't cap you to a certain monthly allowance and once you exceed it that is it. They operate subscriber traffic management which looks only at how much you upload (send) on an hourly basis. During the evenings if you exceed a certain amount of data per hour then your "upload" speed gets reduced for 1 hour till you come back down below the thresholds. The thresholds vary per tier so you can have a look
here and see how it applies to you but the important thing to bear in mind is that you aren't screwed till the end of the month. Your upload speed will be reduced for 2 hours tops and it will only happen in the evenings and weekend so I don't think you need a bb usage meter to watch your traffic (unless you are anal about uploading all evening and not wanting to hit stm).