It looks like the main problem with the Zéfal is that it hugs the bar too closely, and would give you an excellent view of... you. The stem on the Ultra Light is 2" long, which is enough to move the mirror out from in front of your body and give you a view of what is behind you. Mostly.

First off, any parabolic mirror is going to give you a distorted view (the right hand mirror on your car is parabolic, which is why "things in the mirror may be closer than they appear"; which is to say that things look tiny in parabolic mirrors). Secondly, depending on your hand position, you might experience visual blockage from your body. On my handlebars...



...when riding in the primary position, where the hand is aft and very slightly outboard of the mirror mount, my arm blocks about 1/3rd of the mirror (and can be moved out of the way, but it makes the mirror less useful at a quick glance). In the secondary position, up in the bend where the bar tape is and the hand position is forward and inboard of the mirror, no blockage. On the Lady's bike...



... where all hand positions are either inboard or forward of the mirror mount, body blockage is a non-issue. I think that the height of the Ultra Light mirror goes a long way towards making in useful in multiple hand positions without adjustment. The Lady G'Cakes has also run this mirror with trekking bars in approximately the same position (lower left corner) as with the riser bars and bar ends, without any significant body blockage issues. Furthermore, I've never had an issue with vibration with this mirror.