As with the bait, be patient.  Give this a good week before you judge the unit.  After a week, the flys started gathering hardcore.  Best fly control I've ever done around the farm.  We have dairy goats.  Lots... too many really.  And ... 3 months later -- so few flies.  I bought 7 of them and put them all over.  Worked better than expected (after giving it time to work.  I was worried during the first 5 days... but then... then they kicked in).  Go stink.