If you are at appx. 20% body fat, I would recommend a longer cut than 4 weeks. 4 weeks is a very short period of time to see significant change in body composition, and even with the right supplements you don't want to be too extreme with dieting. Realistically, you should aim to lose 1lb per week, so 4 weeks would be 4-5 pounds of body weight lost, not body fat. Have you considered doing a longer cut?
I would recommend aiming for 8 weeks at the least, more realistically 12 weeks. Add in FitMax during the last 4 weeks. Diet and training are the major keys in the success of your cut, but adding a thermogenic toward the end of the cut will give you a nice boost.