Seatbelts wont tighten up.

[NickBW]

I have heard only bad things about using a 4 point harness though becuase they tend to ride up into your gut in the event of an impact. Many of of them even say that the 3points are safer. *shrugs
But that doesnt matter becuase I just went out and I am much taller then the bottom headrest so using a harness that is angled downward wouldnt do me any good.
I have the money I think I will just go ahead and get a new seatbelt for my car. About $110(£61) for a retractable one or, $60(£33) for non retractable.(this is per, belt not as set).
I think the non rectractable ones be great since they stay tight ALL the time unless I loosen it up myself. Cheap and effective.
Not sure about any negative effects of one though...