they do work , but there are too many variables to take into account
the main problem - it is very costly and for a website without a proper bankroll / marketing funds it could be better to use other forms of marketing
don't expect a flood of gamblers waving their money from the get go ,  signature campaigns are more than that:
backlinks , exposure , proof of funds of sorts etc.
and certainly , do monitor the effects of the campaign if you launch it