I think we have to remember that we are not necessarily the target market. To the average Joe on the street, even when paying the Raileasy booking fee, and 10% of the saving, it will still often be cheaper than their favourite site (The Trainline) on long-distance journeys. They're used to fees anyway, as Trainline already has them.
To check the splits manually takes a lot of time and a lot of non-enthusiasts just can't be bothered, or don't want to risk it as they are unsure of the rules and don't want to get caught out like the professor in the Daily Mail or whatever. Rail ticketing is not something where someone can just read a few sentences and know the ins and outs sadly. So, in that respect the site is providing a service that the competition is not, and its possible that people will be prepared to pay for that service.
To check the splits manually takes a lot of time and a lot of non-enthusiasts just can't be bothered, or don't want to risk it as they are unsure of the rules and don't want to get caught out like the professor in the Daily Mail or whatever. Rail ticketing is not something where someone can just read a few sentences and know the ins and outs sadly. So, in that respect the site is providing a service that the competition is not, and its possible that people will be prepared to pay for that service.