Slap straps serve their purpose for your average disc golfer or beach goer. They're also easier for people who don't have a lot of backpacking knowledge to operate and since it's more an occasional use item vs. spending 8 hours in it, you don't really notice the nylon stretch.
For backpacker/camper use though, poly straps are the way to go. Better weight and easier to use for our backpacking/camping hammock systems. I used some tie-down straps I had in the basement for a couple years. Not much different than the webbing that came on my WBRR. Cheap too.
"I ain't here for a long time, I'm here for a good time"
- George Strait