I use this road a lot and usually stop for a break at the tillietudlum pub.the road is ok when quite but is usually busy at weekends with some dodgy weekend motorists.
One of the poorest roads in Scotland for a bike - avoid! badly surfaced, pot-holed, diesel, cow dung, loads of 30mph sections through lots of villages, and absolutely full of slow dangerous sunday drivers looking for the next garden centre or tea shop.
Lots of variety, changes in elevation, great technical bends, scenary isn't exactly good, but nice road, follow "Clyde Valley Tourist Route". Traffic can be heavy as this is so near Glasgow.