my friend who is a super bad ass mountain bike rider has a gravity dropper and swears by them. in the shop he always tells people "if you want to go faster, add weight to your bike and get a seatpost.
so today we put a rockshox reverb seatpost on my bike and i took it for a ride. i gotta say, yeah, it is something.
with the push of a button, i can drop the seat all the way down, so it's like i have no saddle when i'm going down steep stuff. then, at the bottom, when i push the button, BAM, there is a seat underneath my butt. i am at optimal seat height for any trail condition at all times and i don't have to stop. at the end of the ride i was just randomly adjusting the seat to wherever i wanted, just cause i could.
for racers, i dare say you need one. i don't race, but i am really lazy, so i don't feel like stopping and fuddling with my seat post, so i leave it in the middle, where it's just too low to be efficient peddling, and just too high to be comfortable going downhill.
not anymore. i am quite happy with my experience. i will most likely end up with the rockshox, or a similar seatpost. the only problem is, which seatpost to get.
for what it's worth, crank bros has the joplin, which has had many problems with sticking. the rockshox i rode today has a slow rebound, and has some problems. the gravity dropper seems to be the best thing out there so far.