Millers fuel addative might show an economy improvement by cleaning out (and keeping clean) the engine/EGR/DPF. I know I saw fuel consumption improve when I first started using it on a previous car (1.9cdti Vectra - so similar engine to yours); but can't really say for the Alfa because I've used it right from the start. The Vectra was very prone to blowing black smoke out of the exhaust under hard acceleration (it didn't have a DPF); this completely disappeared when using Millers. In my view, although you can't see black smoke from your car because of the DPF, it must still be clogging the DPF much quicker than it would when using the additive. Theory being that as well as the day to day economy improvement, you should get further gains if DPF regeneration is less frequent.