I booked an m-ticket on Monday via the VT mobile app, somewhat to my surprise, as I was expecting to get a ToD ticket, or maybe an e-ticket.
It was a Shrewsbury-Reading Super Off Peak Return, via Newport, and involved ATW and GWR (fare set by GWR).
Instead of giving me options for delivery, it just defaulted to an m-ticket sent to the Android tablet I was using.
I didn't even know if ATW and GWR accepted such tickets booked via VT, but in the end I had no trouble, though ATW wanted to see "page 2" as well as the QR code, to see the ticket type.
The "Activate" process (on the outbound date only) was also new to me.
It's not at all clear what the various options for ticket delivery are, you just get what you are given.
I wanted what I would get on a full web site, ie a ToD ticket, backed up by email confirmation, but that wasn't on offer.
There's nothing on the "Tickets" section of the NRE web site to describe these tickets and the degree of support by various TOCs.