The way I see it is that the agencies tend to be giving me useless information on a daily basis. I get emails offering me A330 command jobs when I'm a low hours B757 FO and that's just the latest example.
I haven't found any of them useful or even helpful when I speak to them. Every flying job I've gone for and had interviews for have come direct from the airlines website. I find this the best source of info and even when my experience wasn't quite what they were asking for at least then you can talk direct and try and convince them to consider you anyway.
Doesn't quite answer your question but that's the best opinion and experiance I ahve on the issue.