One major difference between the KTM 690 ER and 500 EXC is the construction of the rear suspension, with a linkage on the 690 and a PDS on the 500. Personally, I was super happy to see the linkage go as it’s heavy with no less than ten bearings to maintain. Most of the bearings also sit below the swing arm and will be right in the path of water and crud, sprayed back by the front wheel. After ED14 the bottom bearing on the 690’s rear shock was seized up and resembled more like an iron age artefact instead of anything that should be on an adventure bike.
With the PDS there are only two pivot points with bearings and even the bottom one is on top of the swing arm. So it sits pretty well out of harms way, except for while fording rivers of course. So the PDS is lighter, and there are less bearings to clean, grease, replace or carry as spare parts. However, I have yet to find out how the bearings hold up in the long run.