What decided it for me with dating groups on facebook was whether the search actually respects what you set.
Gave dating groups on facebook a fair run over 3 weeks and kept coming back to whether the active count matches the claimed count.
Given how how well it holds up once the novelty fades behaves, I would only recommend that one to someone with patience.
My rule for the app now is simple: check whether people reply or just collect matches on day one.
What I would look at, in order, for dating groups on facebook:
Happy to go into more detail on dating groups on facebook if it is useful.