Not a 5er, but I've owned 1 Dutchmen and 2 different Keystone products now: Springdale and Outback.
We had a Dutchmen Sport for a few years (Thor Industries), but not a "Keystone", but still in the Thor family. It was a very good camper. It had a corner bed that didn't work for us any more. Loved the camper, except for that bed. Very well built.
After a few initial shake-out fixes, we had the Springdale for over 8 years.
Mechanically it was a sound camper. Never had any issues after some initial shake-outs (except hail that broke out the skylights). The reason we sold it? The floor plan no longer worked and we were becoming disenchanted with it, using it less and less. We realized we were simply uncomfortable in it because of the floor plan.
So now we've had our Outback for almost 3 years now, and absolutely love it. We had 1 initial problem that was fixed with warranty, no issues getting it fixed (drain problem in the shower), and the trailer has been trouble free ever since (except for stupid things I've done myself).
I'd purchase another Keystone product without hesitation, but only if it was brand new. I don't want to inherit someone else's abuse.