There are parts of the Plyxon UX I'm not happy with, but I'm *very* happy with how snappy it is.
It is a pain to go back to PL/SQL developer, due to its lack of speed, wall of gray and tendency to crash.
I do hope that the license will include both, and that you aim for Plyxon to take over completely.
Startup:
Plyxon: 1.5s to logon box, then <1s to window
PL/SQL Developer: 3s to logon box, then 4.5s to window stops redrawing itself over and over again.
Btw, I find the logon box annoying in both. I'd prefer to do all my logging on from the connections in the sidebar