You are correct, the shortcut method involves using a phrase to trigger the the Voice for IoT app’s get voice dialog.
The IFTTT method has a few advantages:
1) Direct commands
2) If an android device is left at the location with the hub(s) then google assistant commands can be triggered remotely. Such as using an old android device as a server.
3) Works with google home.
Disadvantages:
1) There can be a delay of a few seconds
2) A little more difficult to setup, and must purchase AutoRemote
3) This method may lock out other Google Assistant commands, such as any command starting with “turn”.