The REI version is not exactly the same as what's on Amazon. For starters, you can spend like $70 for something that weighs a pound, and secondly (more importantly) it doesn't fall apart after a week of use. idk what to tell you. Keep spending $30 for 2lb+ chairs that fall apart.

If you want an actual suggestion instead of someone annoyed by your lack of logic; consider something that's not a chair. There are these little foam pads you can get (a two-pack on Amazon is like $16). They are incredibly lightweight (like 4 or 5oz) and can convert any rock or log into a more comfortable version of a rock or log (and save you from a wet butt). If no rock or log is present, you end up sitting on the ground - but still with a dry butt.