I only rent a small server from them, but I've been happy with their support. Talked to a real human who could help me with tech questions, even though I pay them next to nothing.
(No affiliation.)
(No affiliation.)
The other common cause of issues is things like crypto which they don't want in their network at all.
This will sound like I am downplaying what people have exprerienced and/or being apologetic on their behalf but that is not my intention. I am just a small time customer of theirs. I've had 1 or 2 dedicated servers with them for many many years now upgrading and migrating as necessary. (It used to be that if you waited for a year or two and upgraded you'd get a better server for cheaper. Those days are gone.)
I've only dealt with support over email where they have been both capable and helpful, but what I needed was just plugging in a hardware kvm switch (free for a few hours - i never had to pay) or replacing a failing hard drive (they do this with zero friction). Perhaps I am lenient on the tech support staff. After all they are my people. I've been to a few datacenters and have huge respect for what they do.
On the presales side they seem to reply with a matter of fact tone with no flexibility. They are a German company after all.
I'm a bit wary I'd get lumped in with the crypto gang. A lot of what I'm doing with the search engine is fairly out there in terms of pushing the hardware in unusual ways.
It would also suck if there ever was a problem. The full state of the search engine is about 1 Tb of data. It's not easy to just start up somewhere else if it vanished.