Problem is that I am travelling all around the word (COVID permitting), almost entirely for work. So I NEED to learn about local customs in as many places as possible...
I agree entirely that one should follow local use as much as possible.
However, the phrase about Romans you cite is a bit misleading. Romans were known do to exactly the opposite, wherever they were going, they were imposing THEIR way.
And actually many Romans are still doing this nowadays...
Of course, coming to Rome and not complying with Roman law and usages was even more dangerous.
The situation was strongly asymmetric, so using this phrase (which technically is a correct suggestion for people visiting Rome) for suggesting to comply with local use in places different from Rome is misleading.
Do not believe everything on line.