I have one, 550-610lbs on a 2022 Stumpjumper Evo. Used it for 18 months so far.
In my experience, it’s excellent for changing the midstroke and general dynamic ride height, it seems to have very very little effect on actual static sag. I use mine on an Ohlins ttx along with rebound HSC to quickly change the setup of the bike for different trails, for that it’s really convenient.
E.G I get around 15mm sag at both extreme ends of the adjustment, 550lbs will be almost exactly the same as the 610lb setting.
You can or course still use the regular preload setting to stiffen it up.