Beware the clone Helinox chairs.  Mine was £33 and lasted a whole hour before it broke.  I weigh just short of 13 stones but it was rated higher than that.  If you can bear using a stool, have a look at the Walkstools.  Cost a fortune, but superbly made.
For warned is for armed as they say, and it's not the first time I have heard that too. The issue over the cloned Helinox Chair cropped up on another forum I'm a member on. 
The Walkstool looks a good "doing" something stool i.e cooking, watching a sporting event or rest awhile seat etc but lacks the relaxed, flop in a real chair type comfort I'm after after a long day in the saddle. I have a Helinox Chair one in the post, @ £74.95, we will have to wait and see if it is worth the expense.
Andy