Totally agree.  It seems to be ok for small parcels, but larger parcels causes problems as Simple Delivery does not know the actual size and different carriers have different maximum limits. The "solution" eBay has given me for the latest issue with a parcel exceeding Royal Mail Medium Parcel size limits, is to purchase a label outside of eBay (at a higher cost), manually update the tracking in the order and then request a refund for the unused pre-paid label in Simple Delivery.  No longer "simple".