It worked pretty well for kids. It wasn't very safe for two reasons.

(1) the zip ran all the way to the other tree, then "bounced" back to the middle which was the lowest spot. The "bounce" was pretty strong and if a kid lost his grip he would be thrown into a tree and fall ten feet to the ground.

(2) the zip was a single line. I did not trust it for anyone over 120 pounds. I never considered trying it.

Zips are cool and fun and dangerous. Ideally you will have a safe starting platform, a safe landing platform, and the ride will not be too high above the ground.