Did the Sustrans route 27 a few years ago on my Halfrauds BSO in a day with commuter tyres, Plymouth to Ilfracombe stayed in a B&B then back the next day.
The route is easily done on a road bike or a MTB with slick tyres, there are no real sections where you will need proper off road tyres & there are long sections of tarmac to ride on.
If you are going from Ilfracombe to Plymouth then avoid the bw just outside of Braunton, it’s a narrow trail between to fields & was very overgrown when I rode it. I would carry on past the start of the bw to the road then head South to Braunton.
Stop @ the eco cafe @ East Yarde they do superb food.
When coming South take the route to the left of Tavistock i.e. Mary Tavy, Peter Tavy, etc the other route is IMHO not biker friendly & is quite a climb.