Data point – I travelled from Budapest to Vienna on RegioJet this week. The train was full and had an additional low-cost coach attached.

I was in standard class in the open-plan Astra coach, because the low-cost tickets had sold out when I booked. Being in the Astra coach, I could order from the menu using the app; the advertised free coffee can only be ordered on the app in this coach.

The train left on time at 07:45, and the app opened for food and drink orders at 08:15. I booked immediately, and the order was delivered at about 08:45. Orders are consolidated, and the steward delivered about 10 orders at once (including free coffees).
Although the coach was full, and seating is 2-2 with less legroom than the 1-2 seating in the low-cost coach, the ride was much smoother in this coach, being much newer than the low-cost coach.