I've used Millers Diesel Power Ecomax for many years in a number of E300TDs and the E280 cdi Sports Estate (OM642 engine)
It has never failed an MOT on emissions.
It claims to increase the cetane number (How would I know ?).
It claims to improve the lubricity and the clean-burn of the fuel, thus improving the life of the high pressure pump and injectors
I bought the car with 110,000 miles on it.
It now has 200,000 miles.
It runs as well today as the day I bought it.
Still returns 40+ mpg on a long run.
I've never had to touch the EGR.
What is there not to like ?
Fingers crossed for the next 200,000 miles.