I've just finished fitting a pair of bonnet stays made by our fellow TMer Cain.
He asked me if I would like to try a pair out to test them and his fitting instructions and I have to say that I am mightily impressed.
He has looked at the various shortcomings of the stays on the market and in particular the ease of operation and security of the bonnet whilst open and come up with a very nice solution. Beautifully engineered with stainless water jet cut brackets.

Rubber covered lower ball joint bolted to lower bonnet catch.

Upper water jet cut stainless bracket with sliding collar lock fits to inside of bonnet catch and clips onto ball fitting on top of stainless stay

Stay in folded position clipped to stainless bracket.