You don't need an External Insert if you want to process real time audio with hardware effects, just record the output of your hardware.
The External Insert plug-in is needed/handy if you play audio from your DAW through an external hardware device and record the outcome, because it cares about the latency which is introduced by the additional DA - AD conversion of your audio interface.
Recording a hardware synth driven via MIDI tracks from a DAW also doesn't need the External Insert plug-in but you may have to adjust a possible offset in Preferences > Sync and Caching or manually by shifting notes.
Best,
Klaus