There are lots of threads about flying weight and mounting of add-ons. I just ordered a Tagg pet tracker (pettracker.com) for my P2 with Zen/GoPro. The weight of the Tagg is stated at a little over 30 grams. Add to that my mini ISOD, Immersion Transmitter and soon my Groundstation Air End unit and I will have added around 100g of weight with wiring. I'll probably be velcroing/double stick taping this stuff on near term, but I think I'll get a CF or phenolic board to attach to the P2 to more neatly arrange things. This does not seem like a lot of extra weight, but I was curious about other people's experience.