Though it may seem so simple and straight forward, I have never been in a place that had the toilet paper mounted on it's side. To me this makes the most sense. No hole in the wall with special insert is necessary with a side mount. I have seen the TP sitting on the back of the toilet countless times. Maybe even more than on the holder 'cause nobody like putting a new roll on for some reason.
There will be No reason to argue over which way the TP should be loaded, paper out or in, top or bottom or whichever way you look at it. The old myth being that one way prevents a small child from unravelling the whole roll. By mounting TP sideways, It will catch and rip before the child has the chance to take the whole roll around the rest of the house.
The side mount is a simple, inexpensive wall mounted holder for Toilet Paper rolls. Taller rods can hold more rolls stacked if necessary. I bet the simplicity and efficiency of the side mount will reduce the amount of TP used. Need I say more?