Unless im mistaken, aren't halo lights just accents? If your headlights were a funky color that could be a problem because certain colors won't show up well under them making it difficult to see signs and or obstacles in the road. If they are indeed just accents though, it sounds like the laws they had with underglow around here. No blues, greens etc that correspond to a list of colors used by law enforcement in different categories.
Anyway, im sure that Kojacks comment meant the same thing. They probably won't get you killed but certainly will get you a ticket.
Most of the popular halo kits are illegal and unsafe for a variety of reasons, Chris.
1) to install them you must take apart the headlight assembly. You've just rendered the lamp illegal at that first step.
2) they come in colors other than white. Illegal.
3) you have to glue your lamp back together. Who knows what the out-gassing of the glue will do to the reflective materials or other constituents of the lamp. Is it going to fall apart? Start a fire? Get dimmer and dimmer?
4) I see people running around with only red halos on their headlights and foglights at dusk. Maybe that could confuse an elderly driver? Make them think it's the tail end of a car? Is it impersonating a LEO?
If your lamp comes with a halo and the lamp is tested and assayed to meet the criteria of FMVSS-108, it's a safe/effective/legal lamp.
Real companies make them. Not website cowboys.