How viable is it to use this in place of an actual insulative top layer?
Would I be able to not bring a down jacket or vest for 3 season use?
(Ex: PCT thru hike)
Would you need a poncho rather than a rain jacket so that you could use the No Sniveller like a poncho liner? Would you tuck in the excess material that would hang out of a standard rain jacket into your pants or just bunch it up inside the jacket? Buy the jacket a bit large to have more room for the material?
Are there other wearable sleep systems? I am interested in going with the Nunatak Skaha with the Arc AT (3/4 length bag) with 1-2oz overfill but that would cost $500+ whereas the No Sniveller is half of that.

