I think that they are still paper reservations. The HST sets aren't equipped with reservation screens to the best of my knowledge.
The HSTs do have electronic screens and I believe that they are used.
They were installed during the refurbishment, although XC have apparently only recently managed to get them working!
The HSTs do have electronic screens and I believe that they are used once in a blue moon when the damn things actually switch on.
The set that was on the 12:25 Plymouth to Glasgow on Friday had paper GWR seat reservation labels, so are clearly used in the event of the screens not working. Having said that, most of the time they do work in my experience.