In article , "Ted" wrote:
I have already bought it, but am just curious.

HD had 4 different box connectors. Cheap ones for NM, BX, and BX/AC, and an
expensive one for MC.

The electrical clerk recommended the NM, but that didn't seem right.

It wasn't. Generally speaking, advice from clerks in HD, Lowes, etc. is worth
exactly what you pay for it.

I was
tempted by the cheap BX clamps, but took the MC since I only needed two of
them anyhow.

Would code require the ones labeled MC,

Yes.

or would the BX have been adequate?

No. If the BX clamps were adequate for use with MC, they'd be identified for
use with MC. They're not, so they aren't.