The respective pros and contras. 

Being a batch process, pan coating offers the possibility of precise dosing, repeated applications and very long treatments for slow processes as are typically the dragees : it results in a low yield but high added value. A drum is rather used to process continuously very large volume/amount of products required  less residence time  ; as with the pan, the mass effect is a plus with regards to polishing but a minus for fragile products. Both the pan and drum tends to be clogged by product in the long run, requiring frequent cleaning. The single screw is choosen as a cheap alternative for basic treatments. The Biturbine is aimed at sensitive products where a ligth film application in a very short time  is sougth after.