If I obtain an Online visa for Cambodia enter through Poi Pet do I avoid the 'whole passport page' visa that is the normal 'on arrival' visa, and any other pertinent experience would be appreciated.

There will be no visa stamp. Be sure you make a copy of e-visa which will be needed for departure.

Also be sure you use the official government (.go) website. There is some others that will charge you a service fee.

you wont get the full page sticker with an evisa but you will still get 2 stamps in your passport an entry and exit stamp but still much better then using a full page