I went to Vietnam a couple times. If you hang out downtown in the city, you might get a random Jehovah's Witness or Seventh Day Adventist* try to chat you up. "Oh, we can't do missionary work out in the open, so we just do one-on-one conversations like this". Despite the lack of "Jesus saves, die sinner" signs in Hanoi, you can definitely find Catholic and Protestant churches in Vietnam.
The Western press likes to piss and moan about settler nation missionaries that go, without proper visas mind you, to spread their Western versions of Christianity to the DPRK, only to get deported. So am I allowed to enter a white people country without a visa to stir up trouble and expect no consequences???
I'm the furthest thing from an expert on Myanmar. I get everything I know from Burmese friends. But if you look into the minority people situation, many of them are being heavily proselytised by the worst of the Amerikan type. I don't want the Pat Robertson's the world anywhere near struggling people.
*I'm definitely not saying that JWs and SDAs are anywhere near the worst as Christian sects go.
You're not going to see a JW this deep in the internet, I can promise you that. Long story short, they're like the Scientology of Christian sects, with (probably) more child sex abuse. Really depraved shit, and it's all about power and control of others for the authority figures.
Mega churches are quite a bit more simple - they're grifts. The attendees don't police or abuse each other, you rarely talk with the pastor if at all, there's no real community. There's no real substance to them, just a gathering to recite some bullshit interpretations of the Bible that ultimately leads to more money donated into the "offering" plate. There's no consistent system of personal abuse, which def happens but it's not an official part of the program and more an outpouring of the ideology. They're a very hateful community and I wouldn't trust them with my kids, but they're more like toddlers - mad about things they know nothing about and blaming unrelated things.