The zipper is certainly not as fool-proof as the bottom entry but is solid as far as zippers go. If you sweat a bit in the hammock maybe give it a regular wash as a precaution (salt from sweat + humidity, soon = corroded metal). That has not been a problem for me.
Double bottom is particularly useful - i can get quite cold at warm temps in the early hours of the morning (at about 20 celcius or less) when it is misty/humid and there is a little breeze. Very thin foam (e.g 3-6mm) in the double layer stops that - a little bulky to carry and a little hotter than ideal at first in the night - but very light (e.g. 100-200 grams). Particularly useful if you are going from lowlands up to highlands/montane areas on the one hike. It seems to be the humidity that magnifies both the hot and the cold - cold, dry and still and I can get down to near freezing with the same 6mm foam (but a much warmer bag).
The no-see-um mess holds a surprising amount of heat when conditions are still. It doesn't occur often but if it is hot, still and no mosquito's about (yeah ok!) leaving the mesh unzipped is significantly cooler for the first half hour or so until your metabolism slows down and the excess heat escapes.
I think the decider for me is the flexibility to use light insulation pads easily - if it weren't for that I may well prefer the bottom entry.
Very nice hammock otherwise BTW