I never owned an M2-ATX, however no big issues, as you said, it's best to mount it on insulated standoffs.
I installed the advanced software version and connected the M4 via usb header, I only changed the time to wait to start up. It behaves perfectly. From my experience you have to disconnect /reconnect the power cable for changes to take effect.
Are there still bugs with the psu. From what ive read as long as you insulate it from the case its ok.
I just received mine today and it works perfectly. I currently have it connected on my desk to my motherboard and an ATX power supply using the method described in the FAQ. I've seen a lot of posts about problems and not knowing how to hook it up and shutting down etc but this thing works as advertised so far. I've got a lot more work to do before I install it in the car but I'm pretty pleased.
I've had mine for almost 2 yrs - but, I only use it as a standard PSU (this killed my battery twice my own stupidity). I've seen many a person cry about the M4. I've had one since they came out. Mine powers my monitor 8" lilly, 2 usb hubs, my HD tuner and all the stuff connected to those hubs, NO PROB!! I LOVE MY M4.
For those who fought FREEDOM has a flavor the PROTECTED will never know. Support our troops.