I was given one of the Xtreme versions of this by a co-worker, since he'd ordered 3 (thinking that they'd break over time, but his first one never did)... I used that thing continually at work... my employer was lock-crazy... locks on every door, elevator locks, escalator locks... I likely pulled the keys out about 200 times per day, being on the watch.
The locking knob broke due to the stress of three heavy keyrings (more than 30 keys) constantly swinging as I walked more than 20 miles per day, so I cut it off the cord very carefully with a Dremel because it was abrading the cord each time I pulled the keys out. The bottom part of the plastic part that holds the key ring got crushed and cracked during some heavy work... I cut it off the cord, tied the cord around a small washer, dabbed some superglue on the knot so it couldn't come undone, put the key rings through the washer, and it worked as good as new. 10 years of use and it's still usable. I'll use it until the cord snaps (then I'll install a new cord) or until the spring snaps (then I'll install a new spring).