Stop leak can be a temporary fix for a leaking or blown head gasket but it should not be used as a permanent repair even though the company states that stop leak will permanently repair the blown head gasket.
To permanently and properly fix a blown head gasket you need to have the head of the engine removed and get it cleaned up and have a new head gasket installed on the engine head.
You can replace a head gasket yourself if you know what you're doing but it requires some time and hard work to get at the head gasket and you must torque the head bolts down properly.
A shop will replace the head gaskets for around $800.00 to $1,000.00 depending on how hard it is to replace the head gasket on your vehicle.