Brand Loyalty is a 3 pt quality. It can be purchased (same cost, apparently) at either the product or manufacturer level. At product level, it's heavy pistols, or SMG's, or similarly limited. At the manufacturer level, it's... everything. You get +1 dice with your brand, -1 dice with everything else.
Now, using it for a skill... say, gymnastics (ares). Erm. This makes no sense. Let's try again. Pistols (Ares). Okay. This makes sense, sort of. You get a bonus for pistols made by Ares, and a penalty for everyone else's. Of course, for the pistols skill in particular.... Ares makes rather a lot of guns. Pistols (Taurus) would be a far worse deal, but cost the same. That seems like an argument against it. Would subsidiaries count? If you took SMG (Saeder-Krupp) would H&K apply since it's a subsidiary of SK (Is it? I kind of assumed it was... SK or Ares.). It is a bit of a nonsensical bonus when ... two companies both make a basic pistol, and you get a +1 dice with the one with one stamp on it, and a -1 with the other. Would you get the bonus if your pal convinced you that the sharpie - drawn Ares logo on (another gun from another company) was real?
As a GM, I think I'd nix it, simply because it's rather vague, and I don't want discussions about wether this or that is owned by (company) all the time, or if they make their own version of it, etc. There's more fun things to do with our time. However, if it fit really well with a character concept, I'd probably allow it. That goes for the quality too, btw - I don't like it, but if someone really wanted it and it fits, sure.