R8 allows C5 to be a much better filter. The circuit might "motorboat" if R8 is removed and the battery is not brand new (its internal resistance is high).
I simulated the Talking Electronics spy amplifier:
1) Its high frequency response cuts frequencies above 300Hz. At 3kHz the response is -28dB down.
2) Its distortion is extremely high.
3) Its gain is very low.
4) Its output level drops with elasped time.
I corrected the value of the biasing resistor for the output transistors and made it work much better.
Now the capacitors that cut all the mid and high audio frequencies should be removed.