I may be alone in this, but my experience of even the greenest fascias and gutters is that if I run along them giving them a soak with pure water, then by the time I go back to the start and scrub, the dirt just comes off.
In light of that, I don't use any chemical on them.
Am I missing something? Have other people tried both methods and found TFR speeds things up?
Genuine question, by the way...
Vin