I have two 4.5ltr rapid feeders, these were bought from two bee suppliers and look identical; I can interchange the two lids and two top hats. If I put one of them in the hive and fill it up with 1ltr of syrup within an hour there is bees floating on the surface of the liquid. Removing that feeder and replacing it with the other one and emptying the syrup from the first into the second there is no bee fatalities. The cone that the bees walk down seem to be equally rough, but short of putting them under a microscope I can't tell. I am going to ditch the killer!!