They all must be SFI approved and tested before they can be sold, and are manufactured to the same specification.
A search around here will suggest the value if the 6 point harness,
and prior to that, it was popular to put a small bulkhead feature in the base of the seat to keep you from going forward (tunneling), but that put a great deal of pressure on the base of your spine that was not a good idea.
If you ever crashed hard against a single crotch strap, the future of you functionality would be in jeopardy.
The 7th point originated with a Bonneville car, and the SCTA rule reflects the requirements.