I've got one on my daily driver. But if and when that car dies, I won't be transferring to the 4Runner, because it has the auto-dimming mirror. It doesn't fit the dimming mirror because the bottom isn't flat and straight. A friend of mine broke off the two sliding/extending clips and used double stick tape to hold it on his Acura's dimming mirror. I'll probably put it in my Tacoma. The convex works great, I can see out the sides of the rear glass whereas the factory mirror only gives me what's behind the back glass. The convex used in conjunction with the side mirror eliminates all blind spots on the passenger side.
IMO, whether it looks good or not depends on how big of a mirror you get. I've got a 320 or 330mm (forget the exact size) and fits perfertly in between the sunvisors and extends a bit passed the factory rearview. I got a convex. I think the most retarded and useless one is the flat Broadway that is the exact same size as the factory mirror, which is 280mm I think.