Trainline is a waste of time and question why it even exists. There is only one operator on the route I normally travel which is Virgin. Fares are exactly the same as the Virgin website, so how can they advertise cheaper tickets?
Trainline is a booking site which you can also use to compare all services on a given route. Most operators will only show only their own services, so Trainline is useful for showing alternate routes, which will often be cheaper.