sounds good to me
that's pretty much how I had my previous laptop-based carputer setup. I used a simple dash-mounted momentary switch to turn the laptop on. the laptop turned itself off after external power was cut. I had a cheap DC-DC power brick controlled by a 30A SPST relay (triggered by the car's ACC line) to ensure that the laptop would never drain the car battery.
regardless of whether you use a simple switch or an auto-on module; you still have to wire external power switch leads to your laptop's motherboard (or docking station's power button). have you done this already?