Tried this today for the first time and it felt great! Definitely recommended. Bought 6 cans of shaving foam, squirted 2 down each leg and the last two around the crotch area. Creates a decent amount of foam with just 6 but it's cheap so could do more if you wanted.
It feels amazing putting them on, so thick and creamy. You feel like you're sliding around inside them and the foam creates a kind of suction in the boots when you pull your feet out.
Cleaning up is simple as well as shaving foam washes away in the shower really easily, thoroughly rinse the waders and then hang them upside down to dry. That can take a while though.
If you like rainwear and foam etc I'd say give it a go. Just two considerations; if you have sensitive skin some foam could potentially iritate you if you have it on you for a while, and unless you buy non scented stuff the smell might linger for a little bit. That said shaving foam is usually a more pleasant smell than some substance ls you might use.