I used it for the front brake pads. I posted about it, it was miles cheaper than MB. My car has FSH by MB but pads via ECP fit portions
When choosing a fitter, check their reviews - the fitter's prices also vary between fitters. But do read their reviews as you will get the good and not so good and the rest is luck. I took the car in at the agreed time, they had the pads/sensor/etc, car done while I waited. 100% happy and saved over 200 quid compared to MB prices
More recently I had the rear pads done - I found a mobile mechanic with 100% feedback the cheapest, he got the parts
ECP fitting option is only for the basic bits from what I saw.