New guy here, I've been reading a lot on the forums, and belong to several others, but I don't post much. I've always learned a lot more by reading, than from talking. And fortunately there is always plenty to read and learn here.
I have an Interarms PPK and thought I'd actually post some pictures of what it looks like with the longer PPK/s mags. My PPK is my warmer weather gun, since it is so easy to conceal, and I use a SmartCarry now rather than a holster. With the SmartCarry you can really go minimal on the cover, just a pair of elastic waist shorts and a tucked in T-shirt will do.
She's a little worn since I have been carrying it since '87, but is completely reliable. I don't remember having a failure with it since the ejector broke about two years ago and I replaced it.
The longer mags are exactly one round longer as you can see in the photos. The bottom plate will hook your finger about the same as the "pinky" gripper on the PPK mags. I use mine at the range though, and carry the PPK mags. So far I have gotten three of the PPK/s mags used at gun shows pretty cheap, so they are certainly an option if you want some extra mags.