Hello @vertimbale !
The main information you must keep in mind is that all you need to work with plastics is specific temperature & pressure.
The main differences between the machines is the product output you can obtain.
Injection machine has it’s limits concerning big items, you would need a bigger barrel & more manual pressure. The process is a one-shot
Compression machine also limits the size of wanted product due to the size of the oven you use. The bigger oven, the potential bigger product. This process is also a one-shot
Extrusion machine is quite different as it is a continuous system (as long as you continue feeding it with schredded plastic), in that sense, you can push the limits much further (concerning the size of output products)
Hope it helped ^^