Many products do not work properly when powered by a square wave.
The transistors increased the square wave current to quickly charge and discharge the high input capacitance of the Mosfets.
One IRFZ44 Mosfet can conduct 36A when it has a pretty big heatsink which is a power of 36A x 12V= 432W. Then one pair of them alternate the 432W with a pause when the other Mosfet is conducting so the output power from one pair of these Mosfets driven by the complementary emitter-follower transistors can be 864W.
The transistors increased the square wave current to quickly charge and discharge the high input capacitance of the Mosfets.
One IRFZ44 Mosfet can conduct 36A when it has a pretty big heatsink which is a power of 36A x 12V= 432W. Then one pair of them alternate the 432W with a pause when the other Mosfet is conducting so the output power from one pair of these Mosfets driven by the complementary emitter-follower transistors can be 864W.