Yes, it does work for family share plans. I installed it yesterday and it works fine. I have 5 lines and it shows the total family. You can also choose just to view 1 line if you want. It's a nifty little extension and it doesn't take up too much room.
I will add my YES! to nmchileman's as well. We have 4 lines and it shows me the total for all 4, and I set a flag to notify me when I get within 200 minutes of our 1400. Handy little gadget...kudos to lightninrod for sharing this! You can also log in to your MyVerizon account directly from the gadget....I like this!!