“Therefore, even the MB should/would admit that a baal nefesh can rely on the criterion.”
The MB is not the only one – the Shulchan Aruch HaRav also agrees that a Baal Nefesh should be Machmir:
I will quote his words (345:11):
“??? ?????? ??? ???? ???? ???? ?????? ?? ??? ??? ????? ???? ???? ???? ????? ??? ??????
??? ?? ?????? ????? ????? ??????? ??? ???? ????? “???? ??? ????? ???? ????? ?????” ???? ????? ???? ??? ??? ?? ?? ?????? (??? ??? ???? ????? ???????)
However, We can argue that he is not speaking in a case where there is a Tzuras haPesach..
Also, the ones that are to be Machmir should be consistent with Baal Nefesh as above..