I got one because South Western Railway recommended it in an advert. Once I got it, I found I couldn't buy the ticket I wanted online. Only sesoan tickets.The only advantages I can see are not needing to do encode exchanges and the spped of read at a barrier.
You can buy tickets from the vending machine but they were advertising how to avoid the need to buy tickets at the statuon by using the ITSO.
As it turned out, some of the tickets I wanted couldn't be purchased at the station! The app itself was rubbish, with no bus point. So all in all, what's the point of ITSO? Haha