Happy to see people using that! :) I implemented that Mumble integration while I was at ArenaNet.
So, even if not used for Mumble, it's now a pretty big feature for other 3rd party software. I use it regularly myself.
(For the unfamiliar: gw2taco et al use position/viewport data, I guess, from the GW2 Mumble API to draw an overlay on top of the game with navigational markers/aids.)