In reply to exiled_northerner:
...and to answer your questions, the track on the southside of Loch Affric as far as Achnamulloch is in regular use by the estate so is well maintained, but it's fairly undulating and small hydro scheme was going in at the time, I assume it's completed now. After Achnamulloch and the Trees For Life cottage, over the bridge the rest of the track to Alltbeithe has suffered from some erosion, so the track has some annoying sections of gravel and awkward sized boulders, the boulders especially prevalent the first couple of km after Achnamulloch, after that the track pretty much drops down to the flood plain all the way to the YH with the only concern being the two or three burns immediately prior to the Hostel, if they are in spate....