On the plus side this is the cheapest gauge you can get and almost does what it is suppose to.
There is no way this is usable without taking the schrader valve out and modifying the fitting that screws on to the schrader valve on the fuel line.
The blue fitting has a small stud threaded into the middle of it that depresses the schrader valve. Which it does but the only way for the fuel to get to the gauge and provide a reading is around the threads of the stud which it does very slowly making the gauge as assembled useless. Once you take out the stud with a small allen wrench, take out the schrader valve in the fuel rail, and then screw the gauge on it will be useable.
Being the most affordable gauge on the market it does get the job done with a little work but doesn't work as advertised.