The main problem that I've noticed with some kpop stans is that they think endorsing luxury brands (Chanel, Gucci or any world famous designer you name it) is a personality trait when in fact it's not. Business wise, you're promoting a brand that 90% of your audience cannot afford it. Yeah, it looks pretty in a CV but that's it. Trust me when I say that endorsing a "smaller" more affordable brand is making them more bank than any luxury brand could.
Image wise, I don't see any issues, I think BTS are quite smart in choosing the brands they want to endorse, especially when they combine promoting their own image and music at the same time like that Samsung ad did, that was one of the smartest business decisions I've seen.