Welcome to cruise-chat.
I don't know anyone who has been to Algeria. The thing is that the major cruise lines don't stop there, at least as far as I know. Fred Olson Cruises lists Algiers as a port, as does Saga Holidays. These cruises cater to British guests as far as food, activities, etc. They also tend to be longer cruises. And, the ships are not new.
But I do agree that if I wanted to visit Algiers, I'd feel better about it if it was on a cruise ship.