I never realized why some European autos featured a heel mounted mag release until owning the LC9. As much as we would like to do otherwise, many (myself included) often only have one magazine with us, and that's the one in the pistol. Of paramount importance is that the one magazine we have deliver all of its available rounds were it to be called upon. If it cannot do that at a minimum it is next to useless.
I wanted the LC9 for pocket carry in my cargo shorts in warm weather but found it's possible to inadvertently bump the mag release button, partially ejecting the magazine. That and the fact mine would release the mag with gripping pressure on the base plate left me with a loss of confidence in the piece.
After the above, I got my hands on a Shield and never looked back. My advice to Ruger if they don't want their subcompact offering to fall victim to other designs is recess the mag release to better protect it from actuation from deep pocket carry (really, that's why many of us buy these micro 9's). Design your catch such that modest wear won't cause it to disengage when gripping pressure is applied to the base plate.
Finally, build it out of something more corrosion resistant. After several weeks in an IWB holster during the summer, I found red rust developed between the barrel and slide at the muzzle and in the front sight dovetail. Minor issue there but avoidable.
I would prefer a defensive pistol not have a magazine safety. Such contrivances are for those who don't understand the proper manual of arms when clearing an auto pistol. In the meantime it provides another opportunity to leave you with a useless paperweight if your mag were lost or damaged.
I'm not a huge fan of having a loose takedown pin floating around when dismounting the slide, but again, minor in the scheme of things.
I still have my LC9 and will never get rid of it, but now it's just a backup if my primary goes down for whatever reason.