UAVs, any good?

[Mechta]

They've not been tried out very often in a non permissive environment,

Maybe not recently, but Vietnam wasn't exactly what one might call a permissive environment (ok, so its from Wiki, but its mentioned elsewhere):

The target vehicle was successful enough that Ryan was asked to develop a reconnaissance version of it, which became the highly successful Model 147 Fire Fly and Lightning Bug series which saw extensive service in the Vietnam war.

...and the Iranians having their way with a fancy American drone is another data point

Is there any real evidence yet that the Iranians did more than use a jammer (which may or may not have actually had any effect), and got lucky when the RQ-170 had a flameout in when in return home mode?