I get the point of wanting a direct before and after, but how do you compare a system when no two days are the same? In the 3 years I've had my system up I've varied by several percent per year with nothing changing.
I have the Tigo Optimizers on my string that's on the roof, and I've got a friend with all 3 of his strings with optimizers. I can promise you they do something, but as pointed out if your inverter will bypass a panel with the diode, all you can really get back is a little bit of power from a shaded panel, which isn't all that significant.
So maybe a good way to look at it is I have bad shading with a tree directly south of my arrays that causes shading 3 months of the year. I already have a CCA and TAP, but still haven't added optimizers to my non-roof array because I don't think the gains would be worth it.