How to understand this simple voice-over-laser circuit
The back to back diodes are a bi-directional LED perhaps used as an indicator of over-drive. You could use two ordinary LEDs instead.

Those transformers can handle a more current before saturation than a laser pointer will want.

The transformer is used to step-up the voltage of the signal and to superimpose the AC sound signal onto the DC supply to the laser driver
The approximately 11:1 step up by the transformer is less important than the way it allows the audio signal to be fed into the laser's power supply.