Sadly, the PMR-30 is one of those firearms that either works or it doesn't, ergo you're bound to receive a mixture of feedback on the subject from folks who got a lemon saying it was unreliable junk and folks who got a working one saying how reliable it is.
Your best bet would be to buy one from an indoor range, that way you can test it out on the spot to confirm whether or not it is reliable.
As for the subject of being used for self-defense, be prepared to receive a lot of strong opposition on the subject, as most folks are unlikely to recommend the use of rimfire cartridges of moderate muzzle energy, especially out of a pistol. (Out of a rifle .22WMR will give you similar energy to a .38 Special +P, but out a pistol you're looking at energy somewhere between .32 ACP and .380 ACP.)