I was convinced that I needed it for the hood button support, because the silicone cover for my Edge 520 (which I needed because the Garmin's altimeter would go crazy whenever it rained) made the buttons nearly impossible to press when wearing long-fingered gloves. Then I switched to a Wahoo that on the plus side has buttons in a more accessible place and on the minus side doesn't support customizing what the hood buttons do. So truthfully, I don't get a whole lot of use out of having D-Fly anymore, but I don't regret paying for it.