I'm merely quoting the benefits... dunno if it's true. Apparently it was thought up by some american climbers who started it all on chains in Yosemite Valley.
I've got a 15m long one and apparently 50mm wide. No i didn't try it in the Alps, I saw them at the outdoor show last year and this year in Brum, looked on youtube, thought it was fun then proceeded to find the cheapest one.
I know about the z-pulley set up you could use, but even that cost £45 on some websites! Total rip-off, so when I saw this for cheap I was compelled to get it, plus it came with a ratchet like the gibbons.
Not tried it yet, but judging by other sources, 15m is a touch short, I'm contemplating getting a 25m for a bigger span between the trees, especially in Wolvo, the trees are "elegantly placed" to what seems over 15m apart :/
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"I'm not mad, I just see things differently"No longer
VP 
: But still Vaguely Philippino
FYI: Actions speak louder than wombats