Complete waste of money if you do a proper warm oil change, drain via sump and new filter.
I would only ever do it to revive an old engine with gummed up oil
I done mine the other week flush cost me nothing and like the saying says,I don’t know where you’ve been and the flush cost me nothing as me mate done it
So i just got the oil change with Fuchs supersyn 10/60 as recommended by Opie for the S54 and my mechanic said the oil in situ actually looked fine
Anyway as I had booked in for a service and MOT he changed it anyway and changed the air filter for good measure
I suspect my car is actually overserviced with 11 stamps in all having done 46k miles
Can't do any harm I guess
The mechanic agreed a flush was a waste of time
Sailed through its MOT which is always a relief