When I installed a set of E-3's in my flathead, I was never expecting to see much, if any, improvements in performance.
The only thing noticeable was improved starting.
There may or may not have been other improvements but that would probably have to be determined by controlled testing.
There are those who have never used the product and may call it
"snake oil" but that's OK, it's just their uninformed opinion and should be taken as such.
There are a few independent tests done on Youtube to be looked at, and will allow one to make a little more informed decision as to whether or not the E-3's are worth the investment.
https://www.youtube.com/watch?v=Lvs32oUBuGw
https://www.youtube.com/watch?v=1KHO8RUWpjM
https://www.youtube.com/watch?v=PStrsHD1dc8