I haven't done them for ages but I have improved my calves, arms and shoulders doing feeder sets. I don't want to get long winded and obviously if you don't have it no amount of training will give you it but they are a great approach. They have to be done in a sensible way and rotated in/out. As I posted you want to pick body parts and movements that won't fatigue your CNS a great deal. The key words are pump and burn and I can hear Rich saying those words in my head
I have done feeder sets for something different and as a standalone but I have also done them as part of a syntherol cycle. I know they work because I have done them as a standalone but obviously when combined with syntherol the results will mainly be from the site enhancement. However they were used as a useful method of to get the most out of the syntherol.
In lock down I done calf raises every night and my calves improved over the months. The same for shoulders and doing lateral raises daily. No one is going to grow 3 inches but it's a useful thing to throw in especially if you want to improve a body part. If you want to throw the kitchen sink at things you would combine them with insulin, oral AAS and intra/post nutrition.