I got Vallejo Game Color Tinny Tin, Hammered Copper, Bright Bronze and Formula P3 Brassy Balls. This means that I've got now every metallic colour from deep brown to orange, gold and silver.
Some things I've noticed: VGC Brassy Brass and Bright Bronze are quite close together. Both are a bit more orange and intense as the now discontinued GW Brazen Brass. In a pinch I would choose Bright Bronze as an substitute over Brassy Brass. Whether GW Dwarf Bronze is lighter than VGC Bright Bronze?
Hammered Copper is a very nice deep, reddish metallic. I will use it together with Bright Bronze and P3 Radiant Platinum as highlights in order to create a nice contrast for the muted green clothes of my Skaven. Radiant Platinum is one of my favourite metallic colours, it's between Chainmail and Mithril Silver with a little hint of yellow. It's great as the final highlight for gold or bronze.
P3 Brass Balls is quite similar to VGC Polished Gold but leans more toward the cold side. Not a must have colour, but nice to have regardless.
All in all the Vallejo Golds are all very nice in terms of consistency and cover better than their Citadel counterparts, I recommend them.
I've also found my perfect Skaven fur colour in P3 Battlefield Brown. It's a dark and very neutral brown. It works best with colours like Khemri Brown or P3 Beast Hide, but you can even use Graveyard Earth or P3 Guncorps Brown. However as it is quite dark you need to mix two or three intermediate stages. I just love all of the browns and beiges from Privateer Press, they are more natural than most the Citadel ones but not dull. And their coverage is excellent, again much better as Games Workshop's offerings.
I've also bought this fancy Vallejo mixing bottles. Well, these were kind of a mistake as I just wanted regular empty dropper bottles. But they are sound with their skala, just a bit too big for my needs. But they are perfect when you want thin down a pot of Citadel Wash 1:1 with water to glaze consistency or such.