The Simon kit comes with a second display that you mount where you can see it when filling.

I wouldn’t be without the Simon display, it really helps to mix the correct amount and be able to finish a job with minimal solution left over.

I will explain my slight variation to the calibration process.

Measure from the top of the lid to the water in a full load (I screwed a couple of boards together making a cross shape and filled the tank until it was just touching the board hanging down in the tank). I zeroed out the volume on my controller & sprayed this load out on the ground to document how many gallons the rate controller said it dispensed. If you don’t do this, you won’t know how many gallons to enter when you start the calibration process for the Simon system. You can adjust all the values if you skip my method, but I feel you get a better calibration knowing the precise amount dispensed and you don’t have to go through and adjust all the calibration numbers (there are 20 readings to enter if I remember correctly). The theory on measuring down from the top is that you can fill it exactly the same when you calibrate the Simon system. Keep in mind, it doesn’t matter what amount is dispensed in the first step, you are calibrating the Simon gauge to your flow meter. As long as you’re happy with your flow meter calibration, the Simon gauge will match it. I filled my tank as full as I’d ever want to when mixing a load (a few inches down from running over). After I dispensed that on the ground, I knew what amount to enter for the full amount in the Simon display. I also entered another calibration entry at the nominal full level of the tank (1,530 full/1,500 nominal).

Foam will affect the full tank reading. If you have a bunch of foam in the tank and the lid is closed, it will jump the reading higher than actual. You just need to avoid having a bunch of foam

It just takes just a few seconds for the reading to settle down when filling. I fill full blast until I’m about 10 gallons from my target level, shut the flow off until the reading stabilizes, then feather in the last few gallons.

To someone not familiar with this type of gauge. When you ask how accurate it is, it’s as accurate as your flow meter, you calibrate it to match what you flow meter shows.

I will add that I had a bad sensor when I got my kit. Steve was very good about quickly sending me a new sensor at his cost. Very good customer service.

I have no insight on the other system linked in the original post