I think you'll find that poly vs steel is going to come down to personal preference.
For the most part, polymer guns are just as durable if not more so than their metal counterparts, especially aluminum. Granted, the solid steel frame of a 1911 would probably make a better hammer than a Glock's plastic one, but I can't remember the last time I needed to pound a nail with an awkward $500 hammer
I like both polymer and steel. I have several of each. The steel ones are classic, timeless designs. However, they tend to be heavier. There is a lot to be said about a polymer semi auto that holds 2 and a half times the ammo of a 1911 and comes in at almost half the weight.
Polymer has proven to be durable, reliable, and cost effective. While there will always be a market and a need for a steel sidearm, the modern technology of the polymer pistol has more than proven itself to be the preferred method of manufacturing for the foreseeable future.
It's personal preference, of course. I would see if you could rent one of the pocket 9s to see if you like it before you buy. For me, I never could shoot the little buggers well. I'm a revolver guy if the gun drops below a 4" barrel.
Good luck