I've got an axminster chuck on each of the 2 lathes, one has the "A" spigot jaws, the other "C" jaws - and I have the "A" screw chuck thingy - fortunately this fits both.
I find it absolutely indispensable in conjunction with spigot jaws - just drill an 8mm hole almost to the final depth of the bowl, mount the blank and get the underside done including footring, finish, remove from screw thingy and reverse into spigot chuck, nice and quick.
I've tried making them too, but found that almost inevitably you apply too much pressure to the blank when fitting and start the screw turning. Though I saw on a US site someone using a carriage screw through a spindle for the chuck and tightening it right up with a spanner before mounting it in the chuck - that would be the best way for a home made one.
Chris.