Yep, it's a great bait, and I would certainly agree with some of the excellent previous posts.
Some other baits come and go, but barbel and chub never seem to tire of hemp and casters. Have been using it for 35 years and if I had a pound for every time I've baitdropped it into a river .....well you know.
I don't usually use a feeder on nearbank to mid river Avon swims as I just like to have minimal camauflaged end gear pinned hard to the riverbed with a 1oz pear backlead a yard or so up the line from a semi-fixed inline lead.
I have tended to reverse the amounts of hemp to caster over the years and now opt for more caster and less hemp.
The perfect scenario that is nearly always a winner is to be able to carefully bait drop casters just upstream of the bait with a dedicated rod,..I've observed doubles scoffing the contents of the dropper as it deposits the goodies.
As others have stated, patience is a virtue here, and leaving the fish to really get on the feed to start with will normally get you more, and bigger barbel on the day.
I tend to use arti's in 3's on a hair as they perfectly replicate how casters bunch up inbetween the gravel.
There are of course variations on the same theme, depending on the venue and the angler that all work on their day.
Maggots will, as we all know get the barbel going, but I prefer casters for static fishing as they tend not to get washed through the swim so quickly on a fast river....just wish they were cheaper!
All the best
dt