Turbo plug head technically has less compression than a standard head button. If you cc both standard and turbo head buttons, you will find, the turbo has more volume.
Lower comp= cooler temps-easier to tune. But the design of the turbo head makes up for this in the way and how much fuel is burnt, hence the low end power increase. I have also found turbo heads are far less prone to flameouts, and detonation/pre-ignition.
From that, timing can be advanced more so than in a standard button, they can also be run leaner, and will continue to make power at a point the standard head would be causing the engine to over heat through detonation.
I convert all the engines I mod to turbo buttons for these reasons. Reliability, fuel consumption, POWAAAH!
The hyper 8 ports I mod, I run turbo buttons, as this usually helps with the lack of low end the 8 ports deliver. Also keep consumption somewhat reasonable.
Cheers
Rhys