CAS and Fransens have them pretty cheap and brand new unlike the one from the USA. The idea is it keeps some of the heat away from the float chamber which helps stop fuel evaporating. Yes it does also help if any fuel leaks but to be honest by that stage I imagine the flames would let you know there was a leak. Be aware that the original heatshields are made with asbestos. Also watch out as there are two types to my knowledge. Edited to add yes two types of asbestos but also two types of heat shield.