Hi
@kingfoot, keep in mind that 5mm is the height of the adapter by itself (the red adapter you are looking at). Once you fit the Broadcom WiFi module on top of that it will end up more than 5mm high. I am guessing the total height will be more like 8mm.
If you look at the pictures of that red adapter, you can see it has a raised fixing point for you to screw the WiFi module down. This means the WiFi module will sit quite high, increasing the overall height slightly.
The adapter that i recommend in the guide (the green adapter) doesn't have any raised fixing point. (this is good and bad) This is good because the WiFi module sits lower, giving an overall lower profile. It is bad because you cant easily secure the module onto the adapter. I used electrical tape to secure it down. You could use some kind of glue for a neater solution. Ultimately that is not too much of a concern because once you put the cover back on it is held securely by the cover and is definitely not going to move.
I am not saying the red adapter definitely wont fit, but just want to warn you it might be problematic. Its hard to tell by the pictures, but i am wondering if that raised fixing point might be removable. You might have a better outcome if you can remove that fixing point, and just use glue or tape to secure the module.
I am not sure what you meant when you said "In theory shouldn't any Broadcom E key work?". Were you asking about Hackintosh support for Broadcom WiFi hardware? Based on what i have read, I think the compatibility varies. So its best to stick to a proven WiFi module. Also, we do not really know if the Xiaomi BIOS has a WiFi whitelist or not. All i can tell you for sure is that the BCM94352Z definitely works with Xiaomi BIOS version XMAKB5R0P0502, and i advise you to stick with that.