If you can swim with the FINIS Agility paddles without struggling to keep them on your hands, your technique is probably good enough for power paddles.
Karen has a nice description of how the Agility paddles “test” your technique.
Important caveat: If at any point you develop shoulder pain while using paddles, stop using them immediately!
I received a complimentary pair of Agility paddles from FINIS at Jamie’s swim camp a few months ago. I have no trouble keeping them on, but I still use them occasionally because of how well I can feel the initial “catch” of my stroke. I think of the Agility paddles as feel for the water paddles, in contrast to the Strokemaker power paddles.
I was happy to hear recently that FINIS is now selling three sizes of Agility paddles – small and large, in addition to the original size (now called “medium”). I always felt the original Agility paddles were a bit too small for my hands, so if I were in the market for new ones, I’d get the Large.
One final note: as usual, I find Terry Laughlin’s perspective on this to be overly simplistic and dogmatic.