you will find reviews on here for girls from these sources but not as many and not as easily
the UKP system does not allow for them to be indexed in the same way, Admin has said that he would like in the future to be able to index them but hasn't yet
AW is by far the largest site and you would have to ask why any WG would choose other places to advertise ?
well it could be that they are cheaper or more successful than AW - but girls I've spoken to seem not to think so
(unless you add in all of the AW add-ons) the girls have also told me that Friday Ad seems to generate lots of timewasters. Or it might be that a girl wants to keep advertising local - say she lives in portsmouth but only works in Brighton or only wants to meet a small regular clientele and only advertises when she has a 'space'
Now there may well be hidden gems on these other sites but they are likely to stay hidden