[Chrysalis]

tomato firmware is the best usage monitoring I have seen.

on the shibby build (and I think is same on other variants) you can see live traffic graph of the connection, but that isnt that amazing however what is you can then view a live graph per device on your network, you can also view per interface on the router. On top of that it tallies up internet usage, overall, per device. It can store this data persistently so isnt lost across reboots, power cuts etc. Break down per day or per month. The asuswrt-merlin firmware imported this feature as well although its not quite as good but still much better than average on merlin. To me isp supplied firmware's are miles behind whats possible on a router.