I found them to be more trouble than they are worth. If it's windy and you're not sat in it, it WILL blow away.
If you're using them outside and it starts getting chilly, the air inside condenses a bit and it deflates somewhat. You then appear drunk as you roll around trying to get in and out of it. Although, that bit may not be a bad idea 
You also need to be careful not to put them on anything sharp such as thistles or you'll puncture it.
And if you haven't got an electric pump, don't bother, unless you have the lungs of a hump backed whale.
Although I always found that after a few glasses of wine, the cup holder caused much mirth amongst my friends, due to it having the appearance of a very large cat's bum.
Having said all that, they are comfortable. They have their place, but they are no perfect.