I had one, and I'd say that the inner is pretty much essential. The condensation in most conditions (even dry) is appalling without it, as the ventilation is pants.
They stand up to the wind and rain remarkably well, and are voluminous (capacious, one might say...
). Personally, I think the best feature is the ability to suspend the tent from either an overhead branch, or a length of cord between two trees (much like a ridge line on our beloved bashas). This turns it into a real palace.
However - if you do use the inner, it pitches inner first. This is my major gripe and the reason I got rid of it. Having to pitch inner first in a supremely wet Scottish week was enough to put me off for life. It
is possible to pitch the outer first, by first pitching the outer, then getting inside and removing the supporting pole and then putting the inner up. This, however, tends to leave the outer slightly slack in areas, and is certainly less than easy.
It's great tent, and vast for the weight (but bear in mind that the total weight including the inner is 2.34kg). But if you can ever envisage using it in wet weather then you will find it a lot less impressive.
Jake.