I'm using FOBO (external BT sensor) on one car and 铁将军 internal on another car. I think the 铁将军 is better. Its more reliable and easier to use. The FOBO's in car unit only has sound and light alarm. To find out the actual tyre pressure you have to use their app with your phone.
Actually one of the sensors of the FOBO failed after about 9 months.
The batteries on the FOBO need to be replaced in 8-9 months. The 铁将军 is in my car for 2 years already, still running!