First time going and it was my wife and I. We had a great time, it was challenging and fun. The first two courses could probably be done by most people, but the last 3 courses were tough and require you to be in good shape. TreeUmph has a great training setup before you begin. Additionally, it's very self-guided which makes it that much more fun. If you move faster or slower through the course, you don't have to wait for a group.
There are still plenty of staff around on the trees and throughout the course so you never feel unsafe. Highly recommend giving this a try at least once, even if you're a little scared. Well worth the afternoon. I'd recommend getting in one of the earlier spots though as by the time we left (around noon), it started to get packed.