Hi, Farnsworth -
I ride a recumbent, and mirrors are IMO necessary at least for recumbents since it is harder to turn your head to look behind you than it is on a DF bike. On my DF I can duck my head and be looking behind (past my shoulder). That said, I use a mirror on my Trek as well.
I have two Mirrycle mirrors with Evo mounting hardware on my V3. I am very favorably impressed with the Mirrycle's construction and adjustability. They aren't cheap, but they don't move once set. They also are minimally convex just enough to widen the field of view without creating enough distortion to make judging distances a problem. They also work well at night, which to me is the true test of a mirror. If you can judge an oncoming car's distance in the mirror at night, it's a good mirror.
2008 Rans V3 - steel steed
1984 Trek 620 - old warhorse