It depends on a number of factors including age, genetics, whether or not you are taking testosterone replacement drugs, and your consistency in taking NADZ.
Your testicles will not turn "freakishly" large, and they will not continue to grow forever. The average user can expect roughly 0.7 inches in length and 0.3 inches in width. This might not sound like much, but consider the fact that the average testicle size is 1.4 to 2.1 inches in length and 0.8 to 1.3 inches in width.
Measuring testicles can be extremely difficult, and most NADZ users measure their growth based on how their testicles feel. NADZ users have consistently self reported having fuller, thicker, and heavier testicles after taking NADZ for 3-6 months. Furthermore, individuals on testosterone replacement therapy have self reported little to no testicular shrinkage while taking NADZ.