im running AR's in 5.45, 7.62, TOK all in "dirty stuff".... never had an issue once with it affecting how the guns run.
if you have a good gun/conversion and you shoot it and clean it? theres nothing wrong with the AR set up as it is.
the conversion to the piston style is more about being able to say you can than actual results.
they are "neat" and a fun swap out, but totally not needed.