Errr....No. Hypothetical situation: You have an accident, the car ends up on its side or roof. Which is quicker to release so you can get out of the car/emergency services can extract you, a single point lap/sash belt or a racing harness? The single point, all day, every day.

 

^ This.

 

how about this situation.. you're in a 1970s 4 700kg 4 cylinder car and have the more likely accident of a heavy impact with something heavier, newer and safer..u want ur non inertia reel type seatbelt or the harness? and i think the harness still would be easier to release if you are upside down. Have you ever been upside down in a 3 point? you can't unclick them.

You can't meet minimum CAMS spec in a closed car with anything less than a 6 point cage. The front legs mean you can't license it in any state that I'm aware of (not full rego anyway).

 

This doesn't mean you can't bolt a harness bar between the rear strut towers and have a proper harness installed for your track days. Half cage is only going to help you in the case of a roll over and the help is going to be somewhat limited. You have to have a fairly big off before you'll squash the roof down far enough to cause you issues. More likely you'll spear off the road and hit a wall at the track and squash the front of it in, half cage isn't going to help at all in that case. It's also extra weight to carry around.