It’s great to see them going public. I only discovered their app pretty recently but I use it every time I want to buy a ticket now - it’s much quicker to make an order & I don’t have to worry about losing my tickets 
Funnily enough that’s one of the key points that their CEO mentioned in one of the stories today -
“If you go London to Birmingham, there are 16 different ticket types and 50 different fares,” Ms Gilmartin said, adding that there were more than 25,000 train stations in Europe and, unlike the airline industry, there was no centralised dataset or booking system to handle ticket sales. “We’ve aggregated all the choice on to one app [so that] users can access the network in a simple and easy way,” she said.
Trainline is Britain’s most popular service for buying tickets online and Ms Gilmartin said that she wanted to expand into Japan and North America. She predicted that consumers would buy a greater proportion of their train and bus tickets online. At present, between 60 per cent and 70 per cent of rail tickets were bought in stations, she said. “There’s no doubt more will go online and to mobile . . . Increased utilisation of the network is bloody good for the environment.”
Quote from (paywall) ‘£1bn flotation is just the ticket for Trainline app’ - The Times
Here’s some more coverage of the news -