I don't have a problem with the concept of udev - I just find the details to be laden with papercuts. Needing different syntax depending on which subsystem is interacting with the device makes no sense from a user perspective.

To cover all bases my udev rule seems to need to contain both

  SUBSYSTEM="hidraw", ATTRS{interface}=="CMSIS-DAP", MODE="0660", GROUP="plugdev"

and

  SUBSYSTEM="usb", ATTR{idVendor}=="1d50", ATTRS{idProduct}=="602b", MODE="0660", GROUP="plugdev"

I don't understand why the second rule isn't sufficient, and finding enough information online to even consider trying the first rule was extremely difficult.