Hey Geek,
I have a Benchmade 5000 auto and had a 521. The 5000 has seen more heavy use than most knives ever will and has held up well. My only complaint/concern is with the auto's safety for the Axis lock.
It has broken 2-3 times in 6 years, albeit with daily use. The reason I mention this is the 521 I bought to use as my EDC but it opened in my pocket 3 times. Once, it sliced me to the bone. The axis lock is Super strong and I LOVE my 5000 but wouldn't buy an Axis lock w/o a safety.
Hope I didn't muddy the waters too much.
And one can never go wrong with a Spyderco. Lol