Perfectly legal. It’s not electronic. It works the same as the fiber optic pins on your bow. It has a little rubber strip with even spaced holes in it that you insert small length of fiber optic into. There’s a little sheet with it and available on their page that tells you how to space the pins for which size of game. Check it against known sizes at known ranges. It’s not new technology by any means, same as any mil dot scope. You’re using a known size to estimate distance. In this case it can vary based on things like your draw length because you’d be holding the device farther from your eye, but that’s why you check it.