Why would it be safer? Your just bolting them into the stock position where the rear seatbelt buckle was, if it wasn't safe Toyota wouldn't have made that point on the car for a seatbelt.
I am sorry but if you actually look where your seat belts are bolted in the front or even in the back, the bit that supports you is above your head so yes TOYOTA as you say are very safe, or maybe how every car is. The fact of the matter is when your are running harness's if you have the main harness pointing downwards, when your crash the strain pulls down on the seat which can pull on your spine.
If the angle however is more of a 60 - 90 Degree it puts less strain.
So going back to my main point which was it would be rather annoying running it through rear seats
GLWS Sorry.
I read you would be better off in a crash with a harness bar because it is level with your shoulders and if there attached to the rear seat belt buckle it puts pressure on your shoulders when you crash. Just what I read don't quote me.
Thankyou, and by FIA standard has to be mounted in a virtually 90 degree angle or near enough.
Ralphyyyyy