New external member of security group: user or no user?

I think Vasil's answer is partway there. The choice is between adding a user from the M365 admin portal--not SPO--or from AAD. SPO already has permissions assigned to a security group. I need to add two persons to that group who are not in my organization. In the past, I've added them first as guest users in AAD, and then added them to the group. From the M365 admin portal, that is necessary, because otherwise it appears that I cannot add someone with just an e-mail address; however, from AAD, I *could* add someone to a security group with just an e-mail address. So the question is whether I should just do that, or whether it would be better for some reason to add them first as a guest user.