I am now an infrequent user of e-tickets from Trainline, and they work OK for me. I get an email with a PDF and the option of loading them into my Apple Wallet, which I find useful also.
To be consistent and clear, for my personal travel I'm still slightly in favour of orange card tickets, but I live reasonably close to a station and it's not really a problem going to collect them prior to travel if I want to. If this weren't an easy option I might favour e-tickets.
However I do some work for a charity, which prefers to buy train tickets for me. This allows them to buy tickets consistent with their travel policies, which are generally "advance tickets are always cheaper, so buy these" but they are also reasonable enough to modify this at my request, for example to buy open tickets for returns from London Euston on a Friday.
In the past, when they bought tickets for me, they used FGW and had tickets posted to me. Once, they used the wrong address, that of my neighbour, but I was aware and fortunately able to intercept the post that time. Now they use Trainline and e-tickets and it's much better and avoids this particular problem. I'm off to Nottingham next month for a meeting and already have the tickets, they're certainly cheap, and I'm all set.
It will be my first experience of using e-tickets with an operator other than Virgin/Avanti, but I sense that the e-ticket implementation is now mature enough that it won't be a problem.