Ive always used engine flush on petrol engines with good results, unless its a bad engine it does smoothen it out.
However, and here is the but, I did the same on an
Ibiza SDI diesel and as said above it did start to lose a bit of oil every week, and did rattle on start up, which it did not do before the flush. Incidentally, it burst into flames a few weeks after, but im sure its unrelated!
One important thing is the type of oil, ive now got a PD Skoda (dont laugh, bad
badge, great car) and its got fully synthetic in there. Diesel oils have a lot of detergent which keeps them clean, as well as top quality oil, so flush isnt necessary.
Id keep to the oil change intervals, and if you do think it needs cleaning out just change the oil a little earlier. On mine thats maybe after 5k instead of the usual 10k.