Yup, as mentioned, go black label metal or go home.
The white label metal pots are appaling, there was an issue between the studio testers and the final product that made them not far off unuseable and in some instances prone to exploding (I kid you not!)
However, the black label (they literally have black labels) are mint. As good as teh fabled GW metals of yore

I use them alongside the army painter metals which are also perfect (Army Painter took the best bits of several ranges to make theirs, though I am having issue with their paints being really claggy and thick, guessing its old stock or a batch issue...)
I hear good things about the vallejo air metals, super thin pigment, which can be a real boon for 6mm, as the scale can be thrown out by the metallic flakes being visible in some instances. Not tried them myself, but they certainly are a buzz work at present.
I totalyl agree P3 misses a few key colours, browns are not as comprehensive as I'd like, but they have other colours, like Coal Black and Skorne Red that are just wonderful. Add in the foundry and coat d'armes ranges and you should have all the coverage you will need.