If the village expands it will get replaced, is there space to do it in the existing works or will they need to go elsewhere?
It could also get replaced with a pumping station as the water companies prefer fewer, larger assets
At some point it will need an upgrade, I doubt that would be a trickling filter.
Also ask about flies, these trouble some works,
However remember you can complain about odour etc and at some point it will trigger some actions
Also ask EA regarding the number/type of complaints and the compliance of the works discharge, ask if it is permitted (unlikely but worth asking) if yes then ask for a copy
Finally remember that in small hamlets the alternative is often a septic tank at the end of the garden, you are buying a rural property so you need to view in context.