Wise move....
Not sure I believe it....
Have they already delivered the goods I wonder..?
I do not believe it either.
Maybe Iran no longer ‘needs’ the S300.
Maybe Russia is concerned with what Iran will use them for.
This change of heart came after Iran declared support for Turkey’s ambition to recreate an Islamic Caliphate via Ottoman revival. Russia and Ottoman have many territorial disputes. Russia can deal with a strong Iran aimed at Persian Gulf to keep US busy, but they cannot afford a reviving Turkey working with Iranian support on their border. Russia may change attitude of strong US presence in Middle East.