I've used the capsules just on the hair alongside the boilie. Perhaps a bit more instantaneous and was for very short sessions in a morning before work.
I found that the garlic capsules led to more commons on the bank from a lake where I had caught mainly mirrors.
Kevin Maddocks had a whole chapter on liquid baits in "Carp Fever" - his were injecting sausage skin with liquid attractors if memory serves me right. Food for thought.....
I used to inject the cod liver oil capsules and suck out the cod liver oil (about half) then inject with flavour..............................................