The heat shield's intention is present a barrior between the barrel's radiant heat and your skin.
This, of course, is a trade off because it reflects heat back towards the barrel as a consequence.
I operation, if firing rapidly, but less than 90 rounds in lets say two minutes, then the haet shield allows for more shooter comfort.
However, firing 210 rounds in two minutes, the shield probably resuts in a more negative result.
But also remmeber that the RIS & RAS give you a higher cook-off level than the standard plastic wraps they replaced. So as in most compromises, it ain't all bad news.