Had the Banjo meter for 6-7 years. If you follow the directions for installation, it is quite accurate.

I used to have it on the end of the discharge hose with a male camlock on the input and female on the output. Versatile in that you could hook it into the circuit quickly and move it around. It would meter UAN very accurately as we use our sprayer for top-dressing wheat in the spring. Once I moved to water (with way more surface tension - read bubbles), and then added anything else with more surface tension (Glyphosate is literally a soap), then the accuracy went to heck.

When I set up this last tender trailer, I put the meter on the suction side with 2' of straight run on either side. It costs space, but adds accuracy. The main thing....   one has to subtract the added chemical from the total load now as this is only measuring the 'carrier', not the total volume of solution. As well, after time, you may have to put a 'fudge constant' into your math.

For example: 1000 gallon batch that includes 25 gal of Glyphosate....   From experience, I've discovered that I subtract the 25 gal from the total to come to 975, then subtract 3% from this (meter is about 3% over with water), I will be within 1% consistently - checked on a platform scale.

Oh, and keep bubbles out of the supply side. I have 2 x 2600 gallon tanks I pull from. If you let a tank run dry, it will affect accuracy as well.

Ken