It's minor issue, but this new feature needs better cross-mod compatibility (i believe author of https://www.curseforge.com/minecraft/mc-mods/easy-elytra-takeoff faced the same problem before).

When https://www.curseforge.com/minecraft/mc-mods/curious-elytra mod installed, Better Elytra Rocket doesn't work if you use Elytra in Curio slot. In chestplate slot it works as intended.

To forsee similar requests in the future, this feature probably won't also work with all sorts of custom elytras (like https://www.curseforge.com/minecraft/mc-mods/customizable-elytra).

Custom elytras should work fine, as it checks if the item in the chest slot supports elytra flight. Unfortunately I don't think supporting curios elytra without depending on the mod can be done, but the curios elytra dev is welcome to just copy over the code if they want.