Yes, during the survey process, you'll be able to pick 2 twin fitted sheets for king size mattresses. There will be a small fee for king/cali mattresses, you'll be able to make this selection when the campaign is finished.
Well, we've only give them out to a few guys and all of them love it because it stays clean for longer, it is nice to sleep naked on, and they don't have to worry about weird smells when they have guests sleeping over.
Their girlfriends love it too because of the softness, smoothness (less tangled hair in the morning), and skin benefits.
Flat: A flat sheet is also called a top sheet. It's the flat piece of fabric people in the U.S. typically sleep under.
Duvet: A duvet cover is what people typically buy if they use a comforter. It's 2 pieces of flat sheet sawn together, so you can put your comforter inside and keep it from getting dirty (and requiring a frequent wash).
Fitted: A fitted sheet is the fabric you put around your mattress. It typically has elastic around the bottom so it doesn't slide out while you're sleeping.