After reading the sports trader blog I decided I would dabble again with the betdaq exchange and see how the liquidity had improved.   So far from a week of monitoring it appears that pre-event betfair matches approx 5 times what betdaq does.  In-running the gap appears to be bigger.   I did manage yesterday though to get my 2 lays matched in-running on betfair and profit from the 0% commission offer.  So for now I will continue my experiment.