I owned MZ-5n, PZ-1 and PZ-1p at one time. T MZ-5n was a great camera but my fav was clearly the PZ-1p. Some great features are: Of course the hyper program. 'User" setting that could be setup almost any way you liked as your custom shooting setting (which replaced some of the extra custom settings on the Pz-1 (15 vs 18)). the PZ-1P also had a better grip which was rubberized instead of textured plastic. There was a minor upgrade to the Safox II AF system, a little faster. The mirror lock up is a must have feature and the way the mode button was improved is better on the PZ-1p vs the PZ-1. Also 1/250th X-sync and 1/8000th shutter are big feature upgrades.
If you're looking at getting a used one, make sure you find out the condition of the bottom plate. These were great cameras but had one nagging flaw. The bottom plate around the battery door would often crack if it took a hard knock. The plate was a plastic/resin not metal. So check that before you buy. Parts should be available for both fairly easily but these are older and the parts availablity won't last forever if you need a new bottom plate.
Here's a great link on the PZ-1p
photoSIG » Pentax PZ-1p Camera
The camera also fit in the hand a little better with the improved grip. The PZ-1p has a better fit in the hand than even the K10D. If you've never used the Hyper-program system, then once you learn the camera and the features you'll love how that works. Once set up to your preference, the Hyper program allows quick adjustments without removing your eye from the viewfinder. Unique to Pentax and very well thought out. This camera is very much the film version of the K10D digital.
IMO this camera was the best camera available from any brand at the time. In many ways superior to the MZ-S which lost the Hyper Program. Only dumb feature was the Pana button on the back but just ignore it. MAKE SURE you get the manual!! I can't stress that enough on this model. It has many menus and buried features that you will have to read the manual for to figure out. Without the manual this will be a tough camera to master.
Good luck and enjoy it.