Thanks Chad, I was looking at a small racing rectangle mirror but I notice this one has a nice testimonial from Martin Eberhard.
The short answer is that the Sector 111 MicroMirror is a total success - greatly improved forward visibility, no significant degradation of rear visibility. I thought I would miss the day/night feature, but I don't at all. I recommend this as an upgrade to every single Tesla (and every single Elise for that matter).
-Martin Eberhard, Founder and former CEO of Tesla Motors