This is the only way to travel by train between Moscow/St Petersburg. Tickets for the Red Arrow might be a little more expensive (usually, not always) but the disparity in quality and experience is far greater than the price difference.
My partner and I were in a 4-sleeper carriage with one other person who was a lovely Russian guy we chatted to. Despite being once of the cheaper carriages, it was gorgeous with lots of reds, nice seating, plush curtains, tablecloth, etc. We got a meal, tea and a bed with plenty of blankets. This is really all you need in life I think. Note: food here is not great. If picky bring your own.
It was not too noisy (either from the train or other passengers) and was generally a smooth, climate controlled ride. Despite this I didn't get much sleep AT ALL and spent most of the night reading with my light on, which was not a terrible experience anyway. I do recommend light sleepers or those unable to relax in a foreign bed try to get early check in to your hotel upon arrival as the trip can be quite taxing/exhausting.
Bathrooms, floors and general facilities were really clean and we felt safe the entire trip. Unlike some of the other trains out there (looking at you, Nikolay's Express). Staff were always polite and courteous.
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