They're very often used in commercial construction as they fit quite easily into suspended ceilings. Much more difficult to install in a typical wood framed house. They're not noisy if designed and installed correctly.

@Seabornman Do you know what would "create" the noise? Air passing through the slots, creating a whistle effect? Or something else?

There's nothing wrong with linear slot diffusers although they present installation challenges in typical residential construction as Seabornman noted above. Noise is most typically a consequence of air flow rates exceeding the recommended rates. If you're using a residential HVAC contractor and want linear slot diffusers, I suggest you pay a credentialled design professional to design the system.