The PRO 4 has been by far our best-selling hub, we love the reliability and easy servicing. The only criticism is that engagement is a little slower than hubs from I9 or the DT Swiss 350 (with upgraded ratchet). By using offset free hub pawls, the PRO 5 now has 108 points of engagement. The Shimano HG Steel driver doesn't use offset pawls, so if you ride an ebike or are a pedal masher, this will give you less servicing and better longevity at a cost of losing some of the quicker pick-up. Hope have updated the seals for even better reliability and less drag than the PRO 4 (though we never thought the PRO 4 suffered noticeably from drag). The hubs are still home serviceable and Hope have committed to spare back up for 10 years after they stop production. New springs on the pawls are lighter action for less drag and wider for a more solid connection. Axles and hub shells have been re-designed to allow larger bearings - again with the twin goals of increasing reliability and reducing drag.