Plastic helmets (high-impact thermal resin), if they pass DOT or Snell, are reasonably safe, especially for low-speed scootering around town, but remember that the styrofoam core inside is important for absorbing shock energy. Even if the outer shell passes local impact standards, the thin cores of most locally made helmets (especially the little yarmulke types) would not, IMO, protect you as much as the thicker cores of most foreign helms which pass DOT or Snell. You also get what you pay for in terms of the quality of hardware and liner – the cheaper plastic quick-snap buckles are neither as safe as a double-D ring nor as durable as a metal fastener. The rivets on cheaper helmets quickly rust, and the visors are not scratch-resistant. The liners in better helmets are often removable, allowing you to wash them, which makes for more pleasant wearing, especially since Taiwan is so hot and rainy, and the liners can get sweaty, dirty, or even moldy rather quickly. And better brands often have cheekpads of various thicknesses, so you can swap them for a safer and more comfortable fit.
Also note that you can get a composite shell in mid-priced helmets now. A composite shell, of fiberglass, kevlar and/or carbon fiber held together with heat-cured epoxy resin (preferrably in a vacuum process) is superior because the greater strength allows a thinner, lighter shell to offer the same level of protection. The material will also absorb more impact energy, via delamination, than a plastic shell will. Thus, composites offer better protection in a particularly serious hit.
BTW, your head size and shape will also determine which brands you can wear. Local hats tend to be smaller, and very round in shape.