Anyone with recent experience with Regiojet, especially on PRG-VIE and VIE-BUD?

My wife and I will be on holiday in the CEE and taking the aforementioned routes in second half September. We're deciding between Railjet/EC and Regio. Planning to do the PRG-VIE leg in premium and almost certainly Standard/2nd Class in VIE-BUD.

I've got the gen from Seat61, now hoping to get some recent experiential opinions to update and fill in the gaps. The price difference seems considerable, like Regiojet's about ¼ of the big boys (OBB/CD/EC) if I understand correctly and yet pretty much flexi? So what's the catch? How/what to manage expectations on Regio?