Incline bicep curls are a great exercise but are often butchered and not done in the best way
The benefit of them is that it stretches and hits the long head of the biceps predominantly due to the position of the upper arm being behind the body.
You want to take advantage of this by
1) Fully straightening the arm in the bottom position
2) Only bending at the elbow to keep tension on the muscle through out the set
Check out the Video below for a demonstration as well as an extra tip to make this exercise even harder