IWard61 covered most of it. The bit I would add on free us dating site specifically is below.
What separates free us dating site specifically from the rest of the field is whether 'free' means free to browse or free to talk.
About 40 profiles into that one, the pattern around how much control you get over who sees you became obvious.
Assuming you are not paying, how aggressively it pushes credits at you is where the app gets tight.