This is the single most common piece of out of date advice about Da Nang. TPBank was the right answer for years, and a lot of pages still say so.
Your own bank at home may still charge you a foreign withdrawal fee on top, so taking out a larger amount less often usually costs less than small frequent withdrawals.
Carrying about 3,000,000 VND in cash covers a normal day. Plenty of places take card, plenty do not, and the ones that do not are often the ones worth eating at.