Saw a bit on the Discord server, guy tested the backplate and found that it had little appreciable thermal gain, but the vent hole over the fan made it much much louder. "Unusable without a headset," were his exact words, "cannot recommend unless you exclusively play AAA games with headphones on"
I haven't tested them per se since that is not what I bought the back plate for, but there is absolutely a noticable difference in the heat that radiates off the device.
They give you 2 types of buttons for the back, I own the previous version of the backplate and it comes with those too. They comfy to press but I don't use them that much.