I had a 1991 Attitude, it rode beautifully but it cracked where Tintin40 said. My 1999 Adroit (similar to the one in the pic above, post trek but still built at Chealis in Kein Factory), rode grat and didn't give any problems, but the ride was duller than the 91 model (!). As far as alu goes, both bikes were way better than a Yeti Kokopellio.
For a comparison, I've had a 1991 Merlin, a Ritchey Softail, two DBR Axis Ti and the ride was more inspiring, even if the Kleins were better sprinters. The best vintage bike I've tried was a Slingshot.