iPad in single app mode

Anybody any experience is using an iPad in single app mode? This is something new in iOS6 that allows you to lock the iPad so it can only run one app.

Reason I ask:

My family is spread out around the world quite a lot, me in Scotland, sister in London, brother in New Zealand, another in Houston. aunt in Boston, parents in Ireland.

Parents are in their 80's and pretty frail but i was over seeing them this weekend past and , while I was there, called my brother in NZ on Facetime (on iPhone5/3G my end, iPad wifi his). My parents were just amazed seeing him for the first time in 2 years.

So, I got to thinking, all of us have an iOS device of some kind except my parents who don't have a computer and couldn't learn to use one at their age and physical state (Dad has Parkinson's). But they do have Sky TV so can get cheap broadband.

So I wondered about getting them an iPad Mini and setting it so it can only use Facetime.

What d'you think? Will it be reliable enough so they can just pick it up and use it if one of us calls? Or they can pick u rom their favourites list if I set it up?