Unless you’re using the 450/100 or 450/200 models, which are galvanically isolated, it’s essential to install a BatteryProtect. With non-isolated MPPTs, an internal failure can result in high voltage appearing on the low-voltage side—a serious risk to your system.
A BatteryProtect device is designed to disconnect in the event of such a fault, preventing damage. There are numerous examples where BatteryProtects have successfully prevented overvoltage issues caused by MPPT failures. I use them on all my systems, and in my opinion, not including one is a mistake.