A very long treatise on what I have learned about Speedster mirrors:
First, Tom is right.
But that's true about most of what he writes, not just the stuff about mirrors.
I think the aero mirror was designed to be positioned close to the driver (on the door), as its surface area is pretty small. When you move it way out on the fender, the angle of view gets so narrow as to be pretty much useless.
So usually, if only one is installed, it's on the door, close to the driver.
But if you put one on the passenger side door to match, you now have to turn your head too far to the right to look into it. The long, swoopy mount sets the actual mirror pretty far back. So, when they're installed on both sides, they're usually mounted on the fenders. Of course, this makes the one on the passenger side even farther away and even more useless than the one on the driver's side.
This long, swoopy mount issue could be why some people prefer the Talbot style mirrors and similar models. They're less problematic when mounted on the passenger door.
But there is something of a fix for aero mirrors. Sierra Madre (among others) carries a convex version of the glass - made in (OMG) Deutschland - which fits into the cheapo Chinese repop mounts. (The aeros are in two parts - the mount that screws onto the car and the mirror which is completely separate from the mount). The convex glass goes a long way towards making the driver's side mirror useable when mounted out on the fender. But the passenger side is still pretty much useless.
In my opinion, the aero mirror is one of the few doodads you can stick on a Speedster without screwing up the looks too much.
You see how opinionated we can get around here about something as dumb as a mirror?