I have been training in Korean arts (taekwon do - hapki do - gum do) for about 10 years - specifically Hapki Do for about 6 years. My GM teaches 2 sets of forms during the Gup ranks. We learn one form from each set starting at 8 Gup. I can tell you there is a HUGE difference between these HKD forms and the TKD forms that I have been taught.
Also, I had a 2nd Dan in TKD before starting my HKD training and I can say they are VERY different arts with a common connection in kicking - beyond the kicks, they are NOT the same thing. TKD is a hard, linear and "piston-like" art while HKD is a soft, circular and "fluid-like" art.
Plus, you can visit different HKD schools and notice various differences in what and how they teach, unless they are all part of the same organization. So, don't judge the art from exposure to just one HKD school.