Unknown characters in the serial monitor
You are probably looking at a binary transmission protocol, rather than the ASCII protocol you were expecting. 
You might want to investigate further with the module in circuit to capture successful transactions. These transactions could be generated using the app. Since the protocol seems to be binary, be sure to use a serial monitor that can yield the data in hexadecimal or bin format. 

BLDC controllers I know of use simple ttl-level binary serial communication, with a start-checksum, databyte and stop bit. Many of their protocols have already been reverse-engineered and can be found online. You may want to look up for yours.