problems I see with the seed auger is: opening the probox manually and being quick enough (or good enough memory) to shut it off before it spills over the sides of the hopper below (especially if the auger stops or gets shut off) and always guessing on how far to open the box.  Or guessing the timing of when to rush over to close the seed box while continuing to run the auger and fill the planter in order to clean out the hopper and tube before overfilling the planter.   With no drop tube, you have to pull the trailer up perfectly over the planter box and its a long way for seed to fall especially when windy.  not easy to back up to reposition if you need to get closer with that kind of wagon.  It looks like it would take two people and a lot of trial and error to run it smoothly.  just my observations.