The Galaxy S25 Ultra costs £830.00 new compared with £179.00 refurbished (no longer sold new) for the Galaxy S21 Ultra. Buying the Galaxy S25 Ultra refurbished instead of new saves £281.00. If you want Galaxy AI support and a larger 6.9" screen, the Galaxy S25 Ultra is the better choice. If value is your priority, the Galaxy S21 Ultra offers the stronger buy at a lower price point.