Ultralinear and Triode. What's the difference

The way I hear it on my Cary SLI-80 is that the triode mode is softer, with less frequency extension, the edges are rounded off, the midrange is slighty more pronounced, less bass control and other things related to those issues. I like UL on most music truthfully, but some others like only the triode. Of course, whether you like one or the other has to do with you, your room, and your other equipment. Are you thinking of a specific piece of equipment? Maybe someone can chime in that actually has one?
Rush

Looking at the newer Primaluna integrated amps, there's an option for switching between modes on the fly. Just wondering if it's worth the upgrade.

This'll be a bit of a generalization, but here's my impressions based upon experience; Ultra-linear will yield more power and punch, at the expense of holography. Triode will sacrifice the power for a greater sense of dimension, space and textural nuance. Ultra linear leaves me with the impression of sitting much further back in the performance, while triode brings me in closer and gives me a better sense of where the instruments are on stage. If my tastes were in hard driving music like Rock, I might like the muscle and drive of the Ultra-linear. My preferences tend towards acoustic, vocals, folk, blues..more subtle, sparse arrangements in general, with more detail and nuance than most driving rock. I've found for my tastes I prefer Triode. When I had an amp that gave me the option to switch, I almost always ended up listening on triode. No experience with the amps you are considering.

Hope that helps.