Brands only mean so much. A large brand will have speakers from the very cheap to the very expensive, as Yamaha does. Are the lower end of the lineup speakers of poor quality? Not poor perhaps in the general sense of sounding "bad" but perhaps in the sense that they are the poorer performers compared to others....or they may just sound bad on the other hand. Generally cost does have a fair bit to do with it....better drivers and box construction and finishing generally costs more. A good speaker designer can do well with low budgets, too....if the design makes it to production and marketing....price points do matter. Then a brand's success in electronics may not carry over to speakers.
I've never heard of taga harmony myself, might be more a brand marketed in your part of the world (I'm in the US). We don't see a lot of Yamaha speakers here either (there's even a thread or two discussing that around here somewhere).
Take an individual speaker model on its own merits is the best approach, not the brand name it carries. Altho brand can mean better customer support via warranty, availability, etc.