Haven't tried it but would be interested in hearing the results.
I just wash the roof thoroughly each spring and apply a coat of a common floor wax, e.g. Mop n Glo or similar. Only costs a few dollars, easy to apply and generally keeps the white streaks away for 3-4 months. Can re-apply if needed in mid-summer.
I've considered painting the roof, but I'd still have to wash off dirt occasionally and the floor wax is so cheap and easy...
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL