Train travel using REGIOJET

I haven't, but the man in seat 61 has. Page down to the Regiojet article.
https://www.seat61.com/trains-and-routes/prague-vienna-railjet-train.htm

I took Regiojet from Poprad to Ostrava. It is a private company and you have to buy tickets from them, not from Ceske Drahy (Czech Railroad). They compete with CD, that's why their tickets are usually cheaper. Each carriage has an attendant. You can get free newspapers. You also can buy refreshment and get complimentary coffee. First class have refreshment free. Student Agency buses (yellow) are also owned by Regiojet company. They are changing name Student Agency and buses are now called Regiojet too.

We traveled with Regiojet from Prague to Olomouc, a two-hour trip each way. Purchasing tickets online was very easy; we purchased just two days before traveling (in July) and were able to get discounted fares. We traveled in "Relax" class, as we had been advised that it was worth the fare difference. Service by attendants was excellent! There was a great menu, and food prices were very reasonable. We were provided with complimentary beverage service several times during the trip. The train cars were very clean and seemed fairly new. We would definitely travel with them again.

I've used both the buses and the trains for several years. If you look on the website you can find great views of the different class and seating arrangements. I'd say they're about the same or sometimes better than CD trains but they are a tad more expensive too. But, free unlimited cappuccino and coffee, apple strudel for under 50cents (US), and often air conditioned a bit better than some CD trains. The bus was very nice and took less time than going by train when i went from Cesky Krumlov to Prague. I've also used it within Czech Republic. It'll be great!