Yes, I have. 1971. Watch out for the anti-aircraft fire and SAMs. They'll get you!
Just got back from two weeks in Vietnam. The book I chose to read on my long flights is titled "Hunter Killers" about the F105 pilots who flew Wild Weasel SAM suppression missions over Vietnam. Great book.
I got 2 flights in over Hanoi's Long Bien Bridge. The city center is a No Fly Zone (NFZ) and my P3 knew it. I was only in Hanoi one day.
I took a long train ride to Hue where I flew over the Forbidden Purple City and ancient Citadel, the Perfume River, and ancient temples and tombs. I took a day-trip and flew over the old US Marine Combat Base at Khe Sanh. Probably the first drone to ever fly there.
Semper Fidelis, Marines.
Also flew over Hoi An, and Da Nang was great. Flew the Linh Ung Pagoda and massive Lady Buddha statue overlooking the city.
In Da Nang, I brought my backpack to the Marble Mountains and climbed up through the caves to a tiny perch on the outside of the mountain and launched from there. Swirling currents, trees and no satellites until I cleared the mountain. Hairiest launch and recovery I've ever done.
Flying over downtown Saigon, I met a local P4 guy. Excellent footage there, too.
Overall, I think Vietnam is the most permissive area in SE Asia. I flew their equivalents of National Parks and the Statue of Liberty with permission from local administrators and security guards.
Vietnam is definitely drone-worthy and drone-friendly.