Yes they are worth the money. I have one not that particular one but i have had one for a few years and I like it alot. The whole backrest thing doesn't look loike it would help much but it works great. You can lean back against it and it feels like a chair back, so you dont have to be leaning forward or against a tree all day. I also like mine because the straps that hold the back unclip so if you would want to lean back agaist a tree or something you can.
The only thing that I wish it had was like little 4 inch legs, just so you could sit up. I think that would be a big comfort help when you are sitting there all day, just having you legs below you body not staight out in front of you is much more comfy but o'well maybe they will think of that next.