fuel flow meters are an interesting piece of equipment from an install standpoint. It requires an A&P know-how with the powerplant to install new fuel hoses and the sensor, and avionics to install indicator on the panel and connect to the GPS.
The connection to the GNS 430 is not too difficult if the 430 wiring is clean and not too cluttered. Look at the GNS 430 installation manual. just connect 2 wires to RS232 in and out pins (pins 56 and 57 of the P4001 connctor in the back). Of course , the A&P will need the right sub-pin part (get the right part !!) and a crimper.
Enter the setup to configure for the right fuel flow RS232 protol (usually Shadin).
For the FS450, you have the option of setting the "fuel required" to either next waypoint of the flight plan or final destination (total fule required for all segments)
I found the FS450 dat very accurate and I did not need to change the K factor.