How good is the section from Laggan up the East side of Loch Oich? For some reason I was under the impression that it was quite boggy and best avoided.
Not really boggy as such, but can be a bit muddy in wet weather.
They are currently constructing a new cycleway there, as part of NCN route 78, which will follow the old railway line. I’m not sure if this is finished yet, or what sort of surface it has.
Or you can go along the west side of Loch Oich, following the signposted “Invergarry Link”. This is mostly on decent quality forest tracks, so fairly easy. Though quite a steep hill up and down at Invergarry.