As a dial-gauge freak, this item looks entertaining.
On this bike though, I find that I only really need to know about 3 gears:
#1 so that the bike can get rolling without bogging, but this is easy to find, just keep pushing the shift down until it won't go anymore.
Top Gear (I can't remember if that is 5 or 6 !), but this is easy to read with the stock gearing.. the numbers on the tach '4, 5, 6, 7' are just a little less than the road speed in mph divided by 10. So if the tach reads 5,000 and the speed reads about 48mph, I know that I'm already in top gear.
#4 To get around town... easy though, since #2 and #3 are pretty useless, I just get up to speed quickly from a stop upshifting 3 times and I'm done.
I guess if I were racing this thing and had the corners and gears figured out for a particular track then I could really use a gear indicator..
What I'd really like is a rear shock compression indicator.. you know, it would read out how many inches/millimeters that the rear shock is currently compressed.. now *that* would be entertaining !