The "don't use MS" is merely Mahmoud's opinion. I happen to agree with him, but it's just a "matter of opinion". Some people apparently think that their compilers are "better".
If you're planning to "publish a product", the EULA may be relevant. I understand they're not all the same. Some of 'em allow using tools for "drivers and apps for Windows, among other things" Some, with the "free" versions, leave out the "among other things" and are legal "for Windows" only... so I understand.
I am not a lawyer and this is not legal advice. If it's an issue for you, check it out yourself! "Don't use MS" is not a "rule" with Nasm or this forum, it's merely a suggestion - a pretty good one, IMO. YMMV.
Best,
Frank