No safety issues, but defintely don't leave laptop (and any other easy to sell belongings - cellphone and obviously wallet) openly when you go to the bathroom. And lock kupe overnight.
Luxury doesn't mean much. Unless you take SV.
I was very unlucky with the neighbors.
Agency charges from $2 to $15 more than you would buy at railway station. Such ticket should be in the range of 2,500-3,000 RU one way...