I use a Mooncup and I can feel when it's full and, as I'm pretty sure that I have a run of the mill fanjo, I imagine most other women could feel it too. So, not really needed. Especially as my phone spends a lot of time in the DC's hands. I can just picture it now, in a restaurant waiting for our order to arrive, "ping" "Muuuum, your Mooncup wants to be emptied". 