Snazaroo is not just a product for painting kids faces, it's for painting faces in general. It is a PROFFESSIONAL face-painting brand. It is meant for those hot summer festivals and is BUILT to withstand sweat and long hours of walking about, while being easily washed off at the end of the day.
Personally, I love Snazaroo. It's MUCH cheaper than Ben Nye, and you get a TON of it. (one cake lasts forever, and is only about 8 bucks) It goes on smooth and if you seal it with Ben Nye Final Seal (not the powder, or else it'll flake!) It'll stay ON ALL DAY!! I'm serious.
PLUS! Snazaroo is water based, so it doesn't stain! It washes out of clothes COMPLETELY, while Ben Nye always leaves a light smudge even after washing (unless treated immediately)
In my experience, it works fine on the arms, but if your character is full-body (like most homestuck trolls) I'd suggest making some arm socks. This way you don't have to worry about painting your arms, and can just focus on your face!
Experience: Sollux from Homestuck, helping a friend with Amethyst from Steven Universe