I have done shower heads with it, yes, squirting it into the shower head from the hose end, then leaving it hose end up in a glass. Tippi g Viakaly water back into the hose end when it's all run out, and just repeating this process a few times.
I get it in my Sainsbury"s order, but hardware stores stock it, too. Be careful to wear gloves, though, or keep it off your hands, as it's very harsh on skin. Not blister-harsh, but it may come up red and very dry/a bit welt-like.