I've been using ProSteels on my fretted bass for about 5 years now, and really like them. My experience is that they age gracefully, developing a modern full-range tone without significant top-end loss. I find them articulate and easy to control, so capable of a wide range of tones through technique alone. I also like the piano-like top-end extension when playing in the upper registers. Of course the fashion right now seems to be for more 'traditional' thicker tones that can be easily buried in the mix, so ProSteels might well disappoint if that is the goal.
YMMV
Excellent description that matches my experience.