I am not saying you have to go and spend loads and loads on lids, but it does pay to buy quality. One of my mates was a motorcycle courier, and after crash testing a few lids of his own, he always wore a quality one.

Admittedly with a cage in a car it's not the same as riding a bike, but in for a penny in for a pound right? You wouldnt use a cage or harnesses from a little tried brand, so why a lid?

An example of a cheaper lid may pass a test as stated above, but what is to say all of them will - cheap quality means a potential variance in quality (hence the low price), and is it worth taking the chance?

As said above the 500 quid lid doesnt have materials present that justify it's extra cost, but then does a tubular manifold or a cam profile have it's value derived from material only? It's the development that goes into it - it's design and safety features (ie in situ removeable cheek pads etc etc. You pay your dough, you make your choice!