Be aware the M4-ATX is a full size ATX power supply that is bigger than some complete MiniITX systems.
You MAY be able to get by with the M2 or M3 depending on what you are using and they are MUCH smaller.
Also realize that others have had serious noise issues with the M4-ATX and have had to resort to modifications to make it work for them.
All of these similar supplies have similar support. I believe I have the M3 and it has an ignition trigger as well. When I turn on the ignition it will boot up the machine. When I turn off the ignition it will shut down dependent on the time value I set via a jumper. I think I currently have it set for 2 hours. This allows me to go into the store and the PC is still running so when I come back it doesn't take anything to turn it on since it is already on. You can set it to use your ignition like a power switch but you will want some delay to get beyond the starting otherwise it may shut off while you are starting your car. I plan to have the screens tied to the ignition so they are on when the ignition switch is on otherwise they are off. I may provide an override switch so I can power up the screen when the vehicle is off.