I must admit that I used to be a sceptic of e-tickets/m-tickets, after a bad experience with using such a ticket with Stagecoach in Bedfordshire where the driver of a bus on Route 72 refused to accept a Stagecoach Bedfordshire Dayrider Plus on the Stagecoach app, adamantly claiming it was an Arriva ticket and therefore not valid on Stagecoach buses (how exactly that works, I don't know). However in the last year or so, I've begun using these tickets quite regularly, particularly with LNER. In the last 4 months, less than half of the train tickets I've purchased have been on CCST, with all the rest being e-tickets purchased either through LNER, Avanti or TPE.