Having received a new air speed sensor for my FY41AP out of the blue last week, I contacted Feiyu Tech in case they'd sent it by mistake and wanted it back. I got a nice email from Yin in their service dept today ..
"Hi Mark
Dont worry, you are the right person. We did send you another air speed sensor. because in last cargo, our supplier sent us some bad sealants, make some air speed sensor is not working properly. we are not sure yours is good one. so,we changed it.
and you dont need send old one back,it's ok. and we are sorry for troubling you, hope you enjoy your flying with our items"
Yin
So if anyone else receives one unexpectedly, that's the reason !
That`s good of them, normally their customer service is lets say a little lacking :)