I'm just the opposite. I've never had very good success with the nova
chuck
in expansion mode. I turn everything with a tennon and never had one come
loose. I've broken the wood with a catch using both methods so neither
seems to have an advantage there for me. Do you think our different
experiences are related to our turning methods or just coincidence?

Without having seen each other's turning methods, it's hard to say. : )

I should say that the difference I get isn't so much because the chuck
itself grips better in either mode, but because when I turn in expansion, I
usually have better geometry on the wood. Like you, I've had the tenon
break before the chuck gave out - but the way I use it in expansion, there's
typically more wood behind the grip, so to speak, and I've never had a break
that way.

steve