I have an original Zimmerman autoharp with 'mostly' original strings on it...it HAS to be about 100 years old now, and the strings are still 'ok'....several have broken...but....*shrug*...

if any of you have ever heard Ron Wahl play autoharp (he is GOOD), ponder this:...I met him in 1972 or so at Winfield, just as he was starting to build weird autoharps. There was a workshop, and the subject of changing strings came up...and Ron said, "oh, I never break string anymore...I vaseline them"..."HUH?" says the crowd..."yep", says Ron,"I noticed they always break where they bend around the little steel peg near the tuning peg...so I reasoned it was metal fatigue. And I loosened each one and put a bit of vaseline there...I haven't broken a string in a couple of years"........"....but, Ron, what about sound quality?"............"Well, you've been listening to me play...how do they sound to YOU?"

...so...I have no idea whether sound quality in autoharp strings is even noticable...probably not nearly as relevant as on a fine guitar, but there is some anecdotal evidence of their lasting ....analyze away!