why should I use a H-Bridge

Yes but this is not a half H-bridge it is just a simple high side switch and not a very good one at that. The driver circuit can't be an arduino because it does not have an open collector output. Driving a load in the source is not good because the load current backs off the gate voltage and the FET ends up operating in the liner mode. This = hot.

This is not my design, so I can't comment on its quality. It is from an electronics magazine article on power supplys. My understanding is it is designed to be pulsed on/off to keep the gate voltage high, which may work in an h-bridge driven by a servo board at 50 hz. Not sure where the "not a half H-bridge" comment comes from, as it was never claimed to be such.