It's a brother to the "watts up". When I ordered my 'watts up' meter there was a color choice. Since I choice a color that was basically black and they didn't have any so they sent me a Doc Watson instead. A telephone call to the seller indicated they made a mistake and they replaced the Doc Watson with the correct product albeit not in black.
The service tech didn't explain the difference but did say that the Doc Watson was not for an ebike, it was more suited for the RC world or other electronic applications and the 'watts up' was what I needed.
When it arrived, with the generous help of fellow forum member Liberator, I was able to wire it up and mount it. The watts up provides me with more information than I need but most importantly the information I do need such as AH used, WH used, a constant voltage and amps being used. The other stuff like max amps used and max voltage I don't know enough about to care about.
My 5304 running 4 12V 12AH SLA's will use, depending on speed, around 6 AH on a regular 9 mile run, headwinds will increase that as will an increase in speed. Knowing that I'm pushing to 7 AH or more lets me know that my range is running out and when I couple that with the WH used it gives me a ballpark of whether or not I'm going to have to start pedaling if I go past eleven or twelve miles. Mostly it kind of forces me to slow down on longer trips if I want my range to hold out. According to the vendor the Doc Watson does not have all those features. I never hooked the one they sent me in error up as I wanted to return it.