Shaun,
That certainly answers Paul's question,
I used your method and then with 90 deg volume regions (which effectively gives the same vertices to pick). Keeping the subtended angle of any mapped region <=90deg seems key if 'self intersecting' error is to be avoided.
Using only a 10deg portion of cylinder I expected to be able to get the vertex selection method to work (using field points to find the internal corner of the wedge). I could not and got errors : 'self intersecting' and 'mesh region is not fully contained in the model' and 'included angle between the edges is out of range' depending on what order I did things.
The point about the old Rasna 'revolve' delete shells (y/n) was that is was really really simple and intuituve.
Successsful Mapped meshing tactics are just not obvious (if possible) and will put users off the functionality.