I remember getting them on my XT shifter back in 94 and thing what a load of stupid..Its like, if you need another gear, you push the button and you get another gear, unless you push it and you don't then your our of gears. Simple, if you really need to know, then take a peak at your cluster...
then years later I got a new shifter, and didn't realize how much I actually used it without knowing!
But now I have another new shifter, and its back... but my old ones were numbered 1-8 (ok so I never actually remembered if 1 was low and 8 high, or the other way around, but now all there is is the orange maker, butt it doesn't actually tell you what gear your in, just vague where on the cluster you may be... except still I never know, is right high? or Low? or what? so i just peak at the cluster... (not so easy now I am old and flexible as a fat alu tube)...
overall silly idea... or an average idea that could be done much better...
but you can take tyhem off can't you? (my old XT ones you couldn't, but nowdays you can?)