Uppy Downey posts are great I loved my i900. But they are not all they are cracked up to be and they are very expensive. I paid £250 for my recons a couple of years ago and I bet a £200 seatpost wouldn't get through as many miles as they have with zero maintenance.
I normally find I have my seatpost at one of 3 levels slammed for actual DH tracks middle for normal riding (high enough to go up but low enough to be out of the way) sky high for when I need to get somewhere fast in an xc manner or when going up a really big hill.
Obviously with a dropper post you can ALMOST have the best of most worlds but its only an almost and it comes at a cost (£ and time).
Think about what you want to pay for quality and reassurance or convenience and a pain in the ass (possibly literally) WHEN it brakes.
FWIW I sold my i900 with my old bike and ride happily without one. I will probably get another when the price comes down and they become more reliable.