So this thing does keep your shirt in place... kinda.  You could get the same results from a tight belt.  I'm about 20 lbs overweight and wear my pants a little low, about 2" below my hips.  I am tall 6'5'' and this product did not keep the tail of my shirt tucked in.  Also, when you move and stretch, the shirt does not "reset".  The design of this product does not allow the shirt to move back down into the trousers.  I have only used this product with suits and dress shirts.  It does not work.  Some people say it is good for sports uniforms or referees.  I think it might work with that type of thicker polyester material.