I maintain that salad cream is almost the perfect condiment and can work as a substitute for either ketchup (due to it's acidity) or mayonnaise (due to everything else in it).

(Probably not a good idea to substitute either of them when used as ingredients though)

I think the name and the original intent was for it to work as a vinegarette equivalent since it is primarily oil and vinegar, and while it does certainly work there, I will pick vinegarette over sald cream if given the option. But for anything else where you would have ketchup or mayo salad cream wins.