Last time I had to go somewhere in Germany I used a Flixbus instead of their "high-speed" trains. The fact that I was willingly subjecting myself to a Flixbus, not because of price but because of reliability, really tells you something about the state of trains in Germany.
For Americans: Flixbus a cheap bus service which is often used by people who are not really bothered by social norms.
I've tried them once, and my experience with Flixbus was a disaster. They optimize for cheapness above everything else.
Their drivers can't do anything except scan your ticket and deny entrance if the computer says no. They don't speak any local language or English. Any minor problem cascades in delays of half a day. Their bus stops were druggie/thief zones where I felt really unsafe. After their train was 2 hours late, I was a minute late for my connection. The bus driver saw us running to his bus, smiled, waved at us, closed his door and drove away, showing his middle finger out of the window.
Do people on Grayhound busses clip their toenails in sight of everyone? Is there open drug use? Do people bring bluetooth speakers and party in the back?
In that case, yes, Flixbus is similar to Grayhound.
For Americans: Flixbus a cheap bus service which is often used by people who are not really bothered by social norms.