an Infiniti is classified as a luxury sports car. I think they look pretty cool, and regarding your comparison to a mustang it depends on which 'stang you're looking at anything build before '05 is not really safe or stylish, however the stangs from 05 to present are safe cars. They both have a V6 engine so they get about the same MPG's. the reason i specifically say it's a luxury sports car is because the insuance cost will be more for the g35 than the stang due to it's expensive base price when new.
if you mean dangerous as in, will they go out and race with it and act stupid and get speeding tickets then yes. a G35 is the same thing as a mustang in that way.