I bought the Alite Mayfly. It's the best one i've tried so far. I personally liked it better than the Helinox. It's 1.6 pounds and it's just a little bigger than a nalgene bottle.I wrote a review about it on another yak site, so without sending you somewhere else, i'll copy and paste what I wrote and add the photos I took.
Of course this is just my opinion on it.
For years I drug around those big ol' bulky folding camp chairs so I could have a place to sit my weary rear after a long day on the water. I would also bring it on day trips just to have a place to sit and eat lunch and get a break from my kayak seat. They worked great for what they were for, but again, heavy and bulky. I needed something that was a little easier and lighter. Something that would work on the river and on the backpacking trail.
While at a big box store on a family trip, the girls were doing their thing and my son and I hit the camping section. While looking for some lightweight river gear, I ran across the Alite Mayfly. A little over a pound and the size of a water bottle. I was intrigued and took it out and set it up there in the store. I was amazed how easy it was to set up. I sat down, moved around a bit, then my son did the same thing. We both loved it. Very comfy. I made a mental note and once we got back to town, I went to a locally owned shop and had them order me one.
I have used this chair on the river about 12 times now and haven't had any issues at all. I have it stowed in my dry bag with other river necessities and with easy access right inside my bow hatch. My other chair wouldn't fit in there and was lashed on the back if I had room. It takes about 20 seconds to get out of the case and put together. (I should add the little folding stools are cheap and fit inside there, but my back won't tolerate those things.)
As with any ultralight item, it comes with a price. That price is $100. For me, being able to sit comfortably and without pain,(dumb back) is a high priority and this chair is worth every penny. And on multi-day trips or backpacking where every ounce counts, it's nice to have a bit of comfort where normally we would do without because of the added weight.
There are two kinds alite makes that are small, the monarch and the mayfly. The monarch doesn't have the front leg support and is a rocker type. The mayfly can do both, sit and pivot on the back legs or attach the front for a regular chair feel. They make a larger one that handles more weight, and I believe that is called the Mantis, but this one works in my weight class. Hope this helps some.