One thing I've noticed is transparency plays a huge role in NV performance. I'm sure it also does for glass observing, but in light pollution every DSO is pretty faint in glass.
I don't appear to have great transparency too often but have had some really good nights here and there. Maybe it's something to do with the mountains here. When I lived in the St. Louis area, strong storms would blow through and we'd have some really clean and transparent skies. But here in WV the storms don't seem to be as strong and I think the mountains save us a bit. But also makes for not the best skies or even clear skies too often.
This is an important thing to consider when evaluating NV performance.
One of the objects I noticed this the most on was the Horse Head nebula. Some nights with NV it was barely visible, then the next night it's pretty decent.
So on nights where transparency is no good I switch over to planetary and lunar observing.
A point here is don't judge things on one or two night's observing.