Yep – used it as a return from the Gaick pass a couple of times. It’s part of one of the national cycle network routes, basically follows the line of the A9 from Perth to Inverness on a mix of (relatively) quiet roads and purpose built cycle path.
The bit alongside the A9 from Dalnachardoch (where the minor road from Trinafour joins the A9) to the Dalwbinnie turn is probably the least pleasant.
It’s right beside the road (in places you are feet from traffic doing 50+ mph – not nice in high winds), track often covered in muck and there is a smell of piss and shite by each layby plus loads of litter where mouthbreathing scum have dumped food wrappers down the embankment.
It’s better than the alternative of riding on the A9 and it facilitates a lot of long distance cycles, but as a stand-alone I wouldn’t really recommend it. There is much nicer riding either side of Drumochter – loops from Newtonmore to Aviemore on both sides of the river and similar between Pitlochry and Bruar.