The D1 is definitely not suitable as a replacement for any certified piece of equipment. It's a portable device, not TSO'd, and can't be permanently installed in an aircraft or be used for credit against any airplane minimum installed equipment requirements.
However, it's VERY useful as an additional piece of information that is an additional backup to all of your certified panel. And since it's much easier to fly and understand than a conventional "partial panel" situation, it can help reduce workload when you need it most.