it depends on what they actually intent to do with it once the initial novelty and publicity has worn off i suppose.
many often cite the positives of Christianity - the good deeds the missionaries, the helping of others, community spirit etc etc as the best bit about it, and bemoan the fact that without christianity people wouldn't do all those things, as there would be no organised place in which to do it ... so if these people are planning to perform all the positive acts the church do - and basically be 'the church', just with the actual religion bit missing, then it may be a good thing... it would show all those foolish theists that believe it is impossible to be a good person without god.
basically if they are going to be a sort of charity centre/group then ok, no harm in that really, but if they have just set it up just for effect and to gather and laugh at theists, then i cant see the point.
atheists, on the whole, just want religion to disappear... we want it gone as we believe it has no place in our lives or society any more - so joining a group that's whole purpose is to emulate the church, yet oppose it, is allowing yet more of our lives be taken up by religious dogma and leftovers.