Congrats on the Hx and 53mpg! These lean burn hondas are insanely capable of great FE, just depends on how far you wanna go
As for the MPGuino, there is a company that is going to make a complete kit so you dont have to source anything to put it together, just solder a bit. I'm sure you could even pay someone to build one for you and still have quite a bit less money into it then a Scanguage and be more accurate to boot.
Also I have been working on a obd2-obd2 ecu jumper harness that has all the connections for a MPGuino wired in already so it would be plug and play.