I own a PM9 and a Shield. I am a poster on both forums. I do not recall a lot of negative talk on either forum. They are two totally different guns. As far as reliability goes, neither of the guns have given me any problems. Small firearms can, and will be, a problem for a lot of shooters. Some figure it out and others never do. At the range I work at, I see these guns, from Kimber Solo's, to Ruger LCP's for sale because their owner cannot make them function properly. I can't tell you how many husbands buy these things for their wives because they are "small and cute". After ten minutes of frustration I hand that person my Ruger MK III with volquartsen innards, and their life changes. Then, we start working on how to shoot small guns.
I have made modifications to my Kahr magazines that took less than ten total minutes for all three of them. Kahr does not do it because they want Kahr users to use the slide release to chamber the first round. I want to have the option to very slowly and quietly chamber a round. The mods I did gave me that option. Problem solved. The sights on my Shield I felt were not satisfactory and I changed them to Ameriglo's, problem solved. I also changed the sear in my Shield. For me, a much needed improvement.
Never tell anyone the Shield is the same size as a PM9/CM9. They are not even close. I am a instructor and I carry both, but IMHO the Shield is not a great pocket pistol. It does everything else well, but a pocket pistol is a stretch. I guess it depends on your definition of a pocket. For me, it is lightweight wool dress pants.
As someone previously stated, the trigger systems should be the primary guide to making your choice. If you are a DA fan, look hard at a Kahr. If you lean to traditional striker fired trigger systems with a larger magazine capacity, The Shield may be for you. If thickness is not really a big deal, get the M&P 9 compact. That gun is dimensionally the same size as the Shield and carries a lot more rounds.