If you use it in tandem with fiberglass matting then it should hold up just fine. However, it seems very expensive for 300mL of resin. You'd need at least 2 or 3 to do the inside of a helmet.
Clear resins like that (At least in my experience) take at least a day to gel. If you used it, most of the resin would end up pooling at the bottom of your helmet.