I use the inkbird for a secondary heater because I have had the primary heater fail, this way its totally isolated from the apex and will heat the tank in emergency. Also the old Aquacontrollers used to have the power port get stuck on so it was risky running a heater on anything but the Relay ports, so this may be where others have run a backup controller. but the new apex have all relays ports so there is little risk on running the heater directly from the apex.
BTW you can also program the APEX to make sure the heater does not come on and off too often if you know how to program it correctly. Its called Hysteresis, and you put a delay on or off ini the program to stop it