An Arbortech Turboplane fitted to a nice small compact variable speed grinder the likes of Metabo's WEV10-125 Quick. The bigger 1400-1700w tools from Metabo, Makita & others have much more output power, but also are physically larger & heavier, making them a bit of a handful.
My ultimate carving grinder is the long-discontinued WE9-125. The speeds (3-10K) & lower power (900w) make for easier, safer control. Combined with the old tool's small, bulbous bodygrip makes for one of the safest, easily handled & ergonomically superior carving grinder I've ever encountered. Almost all others commonly have a less comfortable & securely gripped cylindrical body, are larger & heavier than the lovely little Metabo.
They still come up regularly in used guise from the usual sources. What makes the WE9-125 so good as a carver, makes it less than suitable as a metal & stone processing tool, however. Here, power, speed and a secure 2-hand grip become much more important than the little Metabo provides.
The smaller carving combo is more about delicacy & finesse than the brute force & power that larger tools provide.
Arbortech's turboblade is a lovely, (relatively) safe, smooth & secure means of freehand carving & hollowing. Ideally suited to chair & stool seat hollowing I'd suggest, being specifically designed with this particular task in mind. Once you get the balance between tool, grinder speed, angle of attack & pressure correct, progress becomes almost intuitively fast, smooth & controllable. It's the weapon of choice for rapid but controllable gross material removal from just about all the commercial carvers I've known.
A final smooth with a small-format ROS like Metabo's 70mm SxE400 or the equivalent Mirka Ceros fitted with intermediate contour pads with will allow a final finish in no time.