Have had Sadowsky flats on a fretless for over 3 years, that probably has 500 hours of play over that time. Love the sound, and these are amazing strings. But find myself tuning a lot more often on my A and D strings and wondering if it's the tuners or if the strings are having trouble holding pitch - also noticing that it takes longer to center the pitch while tuning…
Otherwise, I'm pretty big on the sound of broken-in rounds, but if playing consistently (and I only gig 15-20 times a year, plus jams and rehearsals, and alternating with the fretless), I'm generally looking to change 'em out at 6-9 months.