I have no knowledge of that tool, I guess most people will just have experience of one hollower. I mainly turned bowls but have started to enjoy boxes and vases so decided I did need a hollower. About a month ago I got the Simpn Hope 6mm carbide (round shaft one, no extensions or extras, from Snainton Woodworking) which was curious at first but once I got the knack it's very good indeed. Saw a demonstrator using one earlier this year so that's probably what drew my attenntion. I Used it yesterday to hollow a thin walled small bowl instead of the normal bowl gouge and it shifted the material very quickly. Hollowing end grain beech and similar is probably hard work whatever you use but the Simon Hope tool does OK. There is also a Simon Hope 8mm square shaft tool which was tempting (and cheaper) and probably easier to use but less versatile.
As I have never seen the Sorby I can't compare so you might well be on track for the best option especially if you want to undercut.