Short fills can be impressive... temporarily. I once got 31.76 MPG out of my Mustang, but the next fill was only 28.95 MPG. One fill over 30 MPG with a Mustang doesn't establish a trend. 8 consecutive fills over 30 MPG... That
may establish a trend.
I don't use "gadgets" to get better fuel economy; I "adjusted the nut behind the steering wheel".
AND I have the
fuel log to prove what I've accomplished.
Your mileage may vary.