Does the mayo flavor come through at all? I hate mayo but love the idea of using it this way.

I hate mayo, too. But this does work and the mayo flavor is muted. If you think of it in terms of the ingredients of the mayo (oil, eggs, yolks, water, etc.), it makes more sense. Essentially, it's like a light batter on the bread that slightly cooks and forms a crust on the outside. The oil and eggs promote browning.

You will not taste the mayo once it's cooked. The mayo will add an extra richness that is hard to describe. This griddling technique with mayo is something I sometimes do with my hamburger buns and it makes one killer burger.