Thanks. I think this UART chip goes a lot higher, but something I noticed earlier is that the Ember chip inside this stick is the EM3581 which doesn’t support USB natively. So, it probably has a fixed UART speed programmed into the NCP code. I tend to use the EM3588 here which has USB internal to the Ember and therefore the baud rate doesn’t matter.
I’ll add an option to change the rate on the Ember.
( and nice find 
).