PFF:Ber Rabbit, I have never heard of a "slap strap". What exactly is that? Why do you prefer that over what came on your mask originally?
It's a neoprene strap. They make two kinds, some slip over your mask strap and some replace the mask strap. It's wide, easy to put on, doesn't twist, doesn't slip if you are wearing a hood (with the exception of some drysuit hoods) and if you are diving without a hood it doesn't tangle in your hair. They usually have an interesting picture on them or the name of the dive shop. Cost is about $13 at a shop the last time I looked but well worth it. You can get them online for about $10.
Ber :lilbunny: