I've owned a PZ-20 for several months now, and had the chance to run several rolls of film through.
During that time it's been 100% reliable. I wouldn't hesitate using it at any event.
I do wish that it had a faster top shutter speed at times, plus the Sync Speed is slower than I like at times. However it still gets the job done.
Since I've only used screwmount lenses on it I haven't missed the Depth of field preview. However it's pretty high on my list when I'm shooting with any newer lenses.