A product service agreement means that they will not deny you the right to have your weapon serviced by the maker for a princely sum.
People get all worked up about "Mil-Spec" and how it is the greatest specification there is, it is ONLY a specification. If you take one part built to minimum spec and mate it with a part built to max spec, you end up with a poor fit.
Remember this, the Beretta M9 is made to "Mil-Spec", you don't see very many people swearing it is the greatest handgun specification in existence.
I spent 24 years in the military, I used to wax floors with genuine "Mil-Spec" floor wax. I had a lot of experience prior to my military service doing floors and let me tell you, the "Mil-Spec" wax was the absolute WORST wax I ever used.
Is it a good spec? Yes. Do your handguards need to be mil-spec? No.
Of course certain things should be "Spec", but when you talk finish, hardness etc..., these things are not as important unless you are putting thousands of rounds through the weapon (for example an IPSC/3 gun shooter) in a year, then yes, these things ARE important.