This is the best way to get to manali.
It doesnt go through the main highway which is in a very bad shape and takes you through one of the most beautiful stretches of roads from Una to Mandi to Manali. It also bypasses Kullu city which is really a traffic nightmare. The road is longer by almost a 100 kms from the main route but the time taken is almost the same. With a good 600cc plus bike the route can be covered within 12 hours. I have personally done this 4-5 times in the last year.