All biodigesters need a regular source of food for it though. A 1cubic metre IBC would need roughly a 20L bucket of food a day. More demanding than my chickens !
However it comes down to ease of use. Sometimes an off the shelf product will have little things included in the design that make for a better overall experience like the macerator in the setup above. The gas also needs to undergo 'cleaning' before use and existing gas equipment may need to be modified for use with biogas.
It is however a great alternative to simply going to landfill.