You will have no idea when the parcel is going to arrive, basically. Once, I've paid for Saturday delivery, and only had it delivered mid-week after. Today, I got the one-hour window, and the driver, by the app, was nearby, but then the status changed to 'parcel couldn't be delivered', and that was it; I still have no clue where it is or when it's coming. The customer service people were polite and helpful, but they have no idea what's going on with a particular parcel. So, be prepared to put a few days aside to sit around and wait for DPD to do what hey are paid for if you choose them.