The guillotine press – where you bring the bar down to your neck instead of the lower pecs – is a great chest developer. But there is risk. Keep these light and under control. This is not a bench press variation to go heavy on. And don't try to set a PR! This is bodybuilding, not powerlifting.
My favorite way to use it is 6 x 6 with 20 second rest periods between sets.
They're one of the most difficult muscle groups to develop, but the cure to your underdeveloped hamstrings might lie in the answer to this question: "Which way do you point your toes during a leg curl?"