The two girdles are very similar however the Jofa girdle does not have the loops for 9k shells to be attached too. I have successfully paired a medium 9k shell with the jofa and it seems pretty snug.
Major differences including the following:
9800 uses regular shells like other girdles
Or jofa specific shells which can zip to the girdle;
9800 has buttons to attach suspenders for use;
The JDP caps are noticbly smaller than the 9k;
The spine guard is hard like the 9k but smaller;
The length adjustment system is quite different, and in my opinion better, than the 9k. Unlike the 9k which is just a double sided Velcro tab the 9800 has two long Velcro strips on each side of the thigh guards. These strips are then looped through a buckle allowing much more customization in term of length;
All the core padding is almost exactly the same as the 9k.
There are no tabs to Velcro your socks to on the 9800.
The 9800 is noticably lighter than the 9k. I would say almost half the weight.
Here are some pictures hopefully they illustrate what I tried to explain as the main differences. The St. Mikes 9k shell is not included.
