Thigh muscle control includes the quadriceps and adductors. It also includes the IT band muscles (which could be thought of as adductors). And it can include the hamstrings, which can also be used as adductors (the inner hamstrings) and abductors (the outer hamstrings.
Note that all of these muscles, except for the muscles with "adductor" in their name, work on or across the knee joint. And bar the vastus muscles of the quadriceps group, all of these muscles also work on the hip joint.
So thigh muscle control is about gaining better control of the hips and knees, or at least it can be.
If your interest in thigh muscle control is completely aesthetic in nature, then thigh muscle control can be helpful since you can learn to activate the muscles you are trying to work on.
Want to develop bigger, more shapely quadriceps, then thigh muscle control can help.
If your interest is more functional in nature, say you want to improve knee and/or hip flexibility, or strength, or to deal with pain or poor function, then thigh muscle control can also help.
The thigh muscle control course teaches you simple techniques for activating your thigh muscles at will. You'll learn to activate your quadriceps, your inner and outer thighs, and in some instances your hamstrings.
You'll also learn to feel these muscles activate.
And rather than just activating them and feeling them, you'll also learn to activate them in a variety of poses, both on two legs and one.
You'll then get to experience first hand when activation of these muscles is helpful, and when it isn't.