For me the biggest advantage of Simple Delivery is that I no longer have to worry about whether the packaging will take an item over the parcel size/weight I have chosen. There have been several explanations on the various posts about how this works but my understanding is that Royal Mail will not check parcels that have Marketplace seller (or words to that effect) on them nor will they charge any additional charges to the recipient. I've sent loads of parcels with Simple Delivery both Royal Mail and Evri and, apart from Royal Mail managing to send a parcel from Derby to London vis Newcastle??, I've not had any problems.