I just overhauled my Rockshox Reverb seatpost, and found out how it works in the process. I own an X-Fusion Hilo too, so after I finished, I got curious and watched a video of its overhaul, so I now know how both seatposts work. In addition, I have a long-term perspective, as I rode each seatpost for about a year.
Design
X-Fusion Hilo
Hilo has two chambers for oil and air with a valve that allows oil-air mix to move between them.
This explains why Hilo sometimes feels squishy – you are supported by an air cushion in the outer chamber.
This also means the top seal is under pressure and any issue there is critical to the seatpost operation.
Rockshox Reverb
In Reverb, the oil is kept separate from the air by an internal floating piston (IFP), which means the seatpost is never squishy, as at any time you are supported by a locked oil column and no air.
Main seal is never under pressure, which means any nicks on the shaft are not a big deal.
More Observations
X-Fusion Hilo
You can get most of the squishiness out of it by pumping it up and down while holding the remote open. At the end, at full extension, pump it with tiny amplitude while keeping the seatpost vertical to get the last air bubbles from the outer chamber.
Hilo is slow to compress at the end of the range – I keep wondering if I am getting the advertised 125mm.
Hilo may have very slow return. The reason is not enough air pressure – mine it was low right from the factory. When adding pressure to Hilo, it must be put upside down and pumped several times, otherwise you risk getting a stream of pressurized oil into your shock pump.
Hilo has cool joystick, which could be engaged in any direction. It uses a cable, which is easy to shorten or replace.
Hilo saddle mount creaks. This can be cured to a degree by a dry lubricant (e.g. dry moly) on the pivot joint cradle.
Rockshox Reverb
Reverb has a bit of rotational play – saddle nose could be moved side to side a bit – a small annoyance.
Reverb button seems to engage at the very last mm of its travel.
Reverb has failed on me after a year of trail riding.
Verdict
My choice of a future seatpost will be Rockshox Reverb.
It failed after a year of riding – bottom seal blew up (good description and photo of the issue) and the pressure was lost. I used blue loctite on the bottom seal’s threads after rebuild, so I have high hopes it will never happen again.
While Hilo is holding up pretty good so far, the oil-air mix design means any failure of the pressurized top seal, e.g. related to shaft abrasion, would make it to lose pressure, and, I am afraid, will not be repairable.