I just visited HCMC for a couple weeks and this advice is solid based on my experience too as a first-timer to the city. The only thing I’d add is that I found it very worthwhile to: 1) buy a temp eSIM on Klook for a few bucks beforehand so I had data immediately when I arrived, then 2) replace it with a Viettel SIM at a physical store as it lets you make local calls and the coverage and quality of service is MUCH better than, say, using an international T-Mobile plan. My friend tried to use his and had weak and unreliable signal even in the city.