Protected Content vs. Membership Pro

I am looking for a very simple way to add paid-for content on my site. I'm just curious as to what the main difference is between Protected Content and Membership Pro?

I did use Membership Pro for a while but am looking for a simpler option. For example, have single pieces of content protected until a user pays for that one piece (no user accounts/passwords needed). I don't know if that's even possible...any ideas?

Thanks