plus its free horsepower, or in other words theres no engine strain or hp loss to produce it
Not free at all, it just shows up as pumping loss.
The engine produces more power (and uses more gas) to make up for what is lost in the turbine. For anything but a very well-developed race system the exhaust backpressure is about twice the manifold boost.
10 psi boost = 20 psi exhaust backpressure.
