A very poor redesign by Kohler. Not that Kohler's older pressure balance spool and mixer was really very good but this new design is worse imo. It's more difficult to set the temperature limit compared to the simple setscrew on the previous version. The cheap, crappy plastic service stops in the new valves also often break before they turn even when using a large flathead screwdriver. The plastic just crumbles away. Just a terrible design.
To be clear, the old Kohler design also had its problems like balancing spool diaphragms seizing up internally and locking the temperature after only 5-10 years of use. This is/was incredibly common and frustrating for the owner though it does eventually make for guaranteed service calls for the plumber. At least that previous design was easy to set up and service. The brass service stops would also sometimes seize but at least you had a chance of getting them loose and they wouldn't break like this new design. Metal vs plastic makes a big difference with certain parts of a shower valve.
In any case, you have no choice once the new design valve is installed but to buy this cartridge to service it. You obviously can't use the old design spool and mixer in the new valve.