I had a little play with winged eyecups yesterday - Avian/Field Optics Research pair for compact bins, and very interesting it was too....
I was using the Nikon M7 8x30 and this was the first chance i'd had to get out with the combination.
Firstly, you have the choice of positioning the ring of the eyecup either below the eyepiece (if you use them extended beyond the second stop) or on the lip of the eyepiece itself. If you do extend them (and don't wear glasses) it is best to pull them out first. If you put the eyecup on in the fully-down position, by the time you've rotated them out, they're likely to be in completely the wrong place. (Or you could mark the right place on the edge if you have the patience)
At first (with the ring on the edge) there was a degree of difficulty with eye position, and i got some vignetting; this was just a matter of a bit of practice though, and a slight re-positioning. I suspect alignment with the exit pupil becomes more critical, particularly on smaller bins.
Once i'd got used to it, i held a view and tried them with flaps up, and flaps down as this is easy to achieve with the rubbery Field Optics model.
I was hoping to test for stray light into the ocular, but conditions didn't favour this.
The overall advantage that i perceived was the immersive view with the flaps up, and hadn't realised to this point how aware i was of the light around the binocular. I can't say i noticed any significant change to the light within the binocular view itself (so stray light was not affecting performance), but the enclosing of that view certainly concentrated the eye on optics themselves - and very enjoyable it was too!
Using them with the ring lower down on the barrel neither did anything for side light or the view, so i discounted that; perhaps on larger bins or in other light conditions it might be worth it, but i couldn't perceive any advantage on the M7s as the wings flare out - with them lower, they were just too far away from the edge of the eyepiece.
The only issue is - with the eyecup ring in the 'proper' position - is that the rainguard can't be used, even with the flaps down. The probable solution to this would be to use a rainguard designed for larger binoculars, as most of the time it just has to rest over the oculars.
I can't say i'd use them all the time, but i stuffed them in the cleaning cloth bag and would say that in brightly lit situations with small binoculars, you may appreciate the difference.