I have some ability to compare with and without them. One roof, with 204 deg. azimuth is 8.1 KW without optimizers. The other 2 roofs are 190 deg. azimuth with 8 KW on one and 6.8 KW on the other. The roof without optimizers consistently outperforms the other 2. However, each roof has different shading issues. All roofs are 6/12 pitch.
Yesterday was mostly a full sun day.
8.1 KW system 37.4 KWH (no optimizers)
8.0 KW system 30.0 KWH (this roof has the worst shading)
6.8 KW system 28.1 KWH (scaling up would be 33.5 KWH)
IMO, optimizers don't do much more than diodes, if anything.
I may see different results in the summer when the tree affecting the worst roof is out of the picture.
Panels with optimizers are 400W Panasonic. Panels w/o optimizers are 370W Sil-Fab.