They do work, but according to a study by the University of Arkansas, result in 2 ½ times tougher meat. The key element to plucking is the 'scalding' beforehand, which is immersing the carcass in hot water for a short period. The actual temperature varies between 52 and 60 degrees- subject to experiment. The hotter the water the easier the feathers come out but also the easier the skin tears. Young birds will be quite delicate and need a lower temperature. Storey's guide to Raising Chickens by Gail Damerow covers the subject in detail.
If you didn't scald your chickens first DenisCooper, that will by why hand plucking took so long. You will need a vary large pot sufficient to immerse the chicken fully without overflowing. It will probably be too big for your cooker so you will need a floor standing burner. This is something we are looking at as we intend to breed for meat next year.