Went to the jungles of Chiang Mai to try this activity on the back of a friends recommendation.
After being picked up about 10.30am, we were taken by minibus up to the hills about 2 hours ago. lovely views along the way.
In the afternoon, we divided our time into a mini-trek to an average waterfall in the area, lunch (which was very basic), and then about 2 hours of actual ziplining. In terms of the last of these, staff were extremely friendly, good-natured and safety concious. Not once did I or any of my group feel any risk of injury - everyone is strapped to safety lines by two seperate stages of harness.
The platforms between each line are quite small - so I was very glad that 3 of our potential group of nine didn't show up.. make sure you book for a small a group as possible.
Some of the ziplines are a bit short, but the longer and higher ones are genuinely noteworthy.
If you want to try a different kind of activity in a beautiful setting, this is the one for you.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.