We have never used the misty mates, but we would never go without our Camel Bak's. Although they don't mist you, they provide you with a steady supply of water which is more important than anything in that heat!
Do you mean the little personal fans with a water reservoir to spray yourself? I saw them last week at the Disney Store in Halifax, about 1/2 the price they were on-property in Orlando (where they are EVERYWHERE, in case you don't get one before you leave). My dh also bought a couple of small ones at The Source (still thinking "Radio Shack"!). Hope that helps.
Yep it was hot when we were there at teh beginning of June--wouldn't look forward to that part of a summer trip there. Although you can be in and out of a/c all day, it's not like you're hiking or something.