Yup, if you use them the right way.
Tie your hair in the smallst bun you can do and put it on, meaby if yo have a lot of hair it will be a problem, but righ if you tie it just right.
They never did for me, because I have so much hair :| But they work fine for other people I know. The hair on your nape will get a little wet but other than that, they seem to work.
Well it depends what ur wanting to use it for... No, it does not keep your hair totally dry, but yes, it does effect your speed if your speaking competively.
Not for me, I either have to use the cloth ones which aren't waterproof or the plastic ones won't fit cause i've too much hair