I try not to change more than once or three times or so a year.
The kb I hated most of all was G800. The joystick broke when it was two weeks old. The buttons started sticking and the paint wore off, the display was tiny and hard to read. I suppose it was a lemon, because lots of people loved 'em. It did SOUND good though.
Longest I ever played one was PSR2000--more than a year, though I didn't intend to!
I have a new one on the way now. This PSR S900 has gotten a smudge on the display.
DonM