I occasionally Ride with a Fella (Work Colleague) who has one and loves it (USE job I think).
He’s had it on 4 or 5 bikes now and is pretty happy with it, however I think it has to suit your riding style.
He’s a “stay in the saddle” kind of rider, fit as a Butchers dog, can gring up almost any climb seated (Where th post doesn’t seem to move much anyway) He’s not a saddle dropper either, will stay in the saddle for every descent/single track section. I think he’s probably faster on the downs for having the USE post than he would be without…
It does seem to save his back/arse on longer rides too I think. When I asked him why not go for an FS instead, his reasoning was simply that the Post “Takes the edge off, cost much less, an HT is lighter and that’s all I need”… seemed fair enough to me…