Why do you need/want one?
Sometimes for me, different road conditions affect my perception of speed (flat/straight vs. twisty). In certain cases, I may be riding by feel and be a bit surprised when I try to shift-up, based on feel, to find that I was already in 6th. Then I figure out I was going a bit fast
. I guess looking at the speedo would cure that and a gear indicator wouldn't help...