I snapped up a bunch of these when they first hit C&R status. Here's my brief impression. I've shot two of them.
Bottom Line: It's an okay choice in gun and caliber, but far from the best. For anyone on a very tight budget, and only able to afford rock-bottom defense, this will do. But they are essentially the same size and weight as a small modern 9mm pistol such as Glock, CZ, Kahr, etc. In short, if you are employed, you can do better than the P64. I do love the P64 for what it is, a cool piece of history in a functioning pistol. But probably not a top choice for carry.
Mine were very accurate and reliable. The tiny serrations make it hard to rack the slide. No slide hold open lever. Small risk of slide bite due to small dovetail. Sharp and snappy recoil, much more noticeable than the modern offerings I mentioned.
The stock trigger spring must be replaced because the factory 24 pound is uselessly heavy (hard to pull, and creates inaccurate shooting). The spring is about $10 shipped, and easy to install yourself by watching a Youtube video.
Should get something in the 18 or 20 pound range. This really isn't optional, it's strongly recommended and makes a world of difference in usability.
The 9x18 HP is an adequate self-defense round, but I'd much prefer relying on at 9x19 HP. Ammo prices are comparable.
Total price is going to be around $250-300 after gun, taxes, shipping, FFL, and new spring (less with a C&R). So, again, used modern guns are marginally more expensive, and much more useful. If you compare the size, weight, and thickness, you'll find it to be marginally thinner or the same dimensions as modern carry guns, but the all steel weight is heavier. Oh, and you only get 6 rounds of 9x18 versus the same or more round in larger calibers with modern pistols. The P64 is a cool, fun little curio and would do the job, but just not as well as modern offerings.