I make no claims for the rightness or otherwise of their cause, but they've certainly brought it into the spotlight.
In a sense they've served a useful purpose by showing just how disenfranchised people are, and how to bring attention to any cause you might want to champion - they couldn't find a way to bring about a change in the law by going through official channels, or by organising legal, conventional protests, so they dressed as Batman and climbed Buckingham Palace. And now everyone knows who they are, so although they haven't actually got the law changed, they've at least got people talking about their cause.
Basically, if you want to bring about a change in the law, don't lobby your MP, organise a march or try to arrange meetings with officials from the relevant ministry - that all takes too long and will probably amount to nothing. Instead, dress up in a silly costume and climb something you shouldn't climb, or chuck things at Blair from Strangers Gallery, or whatever. Fathers for Justice, along with groups like the Countryside Alliance, are showing the way forward - intelligent discussion of issues will be abandoned, to be replaced by the politics of the publicity stunt. The groups that can shout loudest will be the ones who are noticed.