One consideration is whether or not you use specs when observing. I had a chance to compare the Nikon 17mm, the Ethos 17mm and a type4 nagler 17mm. The other observers present found the ethos and nikon slightly sharper and with better contrast than the nagler - but I found the opposite as only the nagler had enough eye relief for me to wear my specs.
There wasn't a lot in it, really, they're all exquisite eyepieces.
Cheers,
Andrew.
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