I did an experiment using NuFinish on half of my trailer and Meguiars #50 on the other half. Both looked shiny but the NuFinish half was blotchy in sunlight and didn't last as long. Maybe not scientific but convinced me. I am going to try Meguiars Flagship cleaner/wax this year to compare the finish as Meguiars claims it is a better product on fiberglass.
As for Rejex I tried it some years ago and while it did seem to make bug removal easier in the front I didn't see any improvement in the shine or finish and it didn't last long.
"Your results may be different" :D