The eye relief is a little weird. The eyepieces are DEEPLY recessed when the eyecups are down. They seem to have an "eye box". I've read about eye boxes on the forum and first experienced it with the Bushnell Legend 8x42 roof. With most bins, there is one eyecup position that works best for me with my glasses. In some cases, the adjustment is very precise and only one position works well. With the Legends, almost any position works. With them all the way up, I can't quite see the entire FOV, but any other position works OK. The Vixen are kind of like that. The eye cups have only one detent half way up. Anything from down to the first detent seems to work OK. I finally settled on down as the best, though. That is surprising considering the 20mm eye relief.
I'm not going to say that they are as good as the Superior E's! Even if I believed that, I'm not dumb enough to say it. I suspect everyone would just assume that I don't know what I'm talking about. I suspect that's what people thought after my enthusiastic review of the Brunton Echos.
I'm not a sophisticated reviewer. I'm 53 years old, near sighted, oblivious to CA and wear progressive bifocals. I am visiting relatives on the east coast for the holidays, so I don't have a monpod or tripod to steady them for checking nuances. But I do own high end bins (Zeiss FL T*, Leica Ultravid, Nikon E II, etc) and I know a beautiful view when I see one. I'd like to use the Vixens in good light before passing final judgment on them.
The only thing I don't like about the Vixens so far is the diopter. It doesn't lock and it moves too easily. It is also the first "fast focus" diopter I've encountered. A small movement makes a big difference. On the first day, I inadvertently moved the diopter a small amount. The right side was so blurry, I thought I had a rain drop on the eyepiece. I thought that this was going to be a big problem, but I made it through an hour or so of use the next day without moving the diopter accidentally. It's probably something I'll have to remember to check every time I take them out of their case, though. There is an up side to the fast focus. If you bump the diopter, you'll know it right off.