The mare that my horse used to live with always wore a Kensington fly sheet. I could not believe the quality! She wore it 24/7 and my boy tried to groom her through it all the time. It held up very well to his chewing and biting (she had it for years). It was made out of a mesh similar to a fly mask, but more durable. They do run around $100 though. And I don't think they have belly guards.
I just started my fly sheet shopping this winter too.
Trying to see if I can catch a deal. I've been enjoying my horse's clean coat this winter and am thinking maybe a fly sheet will keep him cleaner in the summer.
As for the fly leg wraps, I think they're ridiculous! They don't seem to provide much protection and I bet they twist around and rub a lot. My boy gets his legs nice and muddy anyways...natural fly protection!