Hi Steve,I think we all understand the mechanics of how it works,and why,but in low water levels,low oxygen levels and high temperatures barbel in particular are extremely spooky would you use one,if I fished the H.Avon during summer I wouldnt use a feeder,most fish I caught on the river in those conditions,I fed once every hour and a half with a dropper and used a straight running leger rig,many times a swan shot link,never with more than 6 swan,usually 3/4 cast alongside streamer weed,sometimes forced to use up to 2ozs,but that was with 6lb line,when I fish the Stour these days I normally use 1.5oz,sometimes 2oz,very occasionally 3oz leads with proper line,feeding via small pva bags,normally casting underarm to feather the plop,plus leaving each cast for at least 40 minutes if possible,casting a 3oz 2" plus diameter feeder with probably 2ozs of bait onboard every 10 minutes would result in any self respecting barbel to disappear into the dense weed,never to be seen again,even on the Wye,unless you experience different,a differing story however if the water was normal level or higher with colour and moderate temps....however nothing is written in stone,that is why bouncing meat will always catch odd fish.