There is so much action that you can get through apps in HCMC that you might not even want to go to any spa or cruising areas, which by the way are not as good or as big as in some other Asian cities like Bangkok or Taipei.
Get yourself a big Airbnb place and you can even set up some group action, way better than at Nadam. Viet guys are pretty wild.
I mostly used Grindr and Hornet and in both the number of guys in Saigon was quite good, even by having a 18-25 age filter.
I remember seeing lots of guys on Blued too, but I don't use that app that much as I consider its UI a bit clunky. Never used Romeo or Scruff in Asia.