Cheap bulbs/ projector housings are illegal because they are not DOT rated, tho there is no law that officially states they are illegal, but without the proper projector housings they are too bright and will blind other drivers ( not dimming for a cop will get you pulled over ) Aiming them down a bit helps, but defeats the purpose of the HID ( projecting the beam farther ).
Parts do not have to have a DOT stamp directly on them as long as they conform and are certified. the lens itself is usually marked with the DOT cert.
I have been blinded more than once by miss aimed HID's, one of those times did almost cause an accident. and I will NEVER install one of those kits. The only upgrade I do to some of my vehicles is 4000K Halogens. FWIW, I drive everything from my '51 Chevy at night ( 6v ) and used to drive the '74 Beetle I had nightly to work and back, and never had any trouble seeing with only low beams. My truck is my current daily, and it just has stock sealed beam halogens in it.