I was interested in Netcup for their dedicated-core vservers (they call them "root servers" although it is a kvm instance on bare metal - probably overprovisioned so also not really dedicated cores). What is your overall experience with them?

Which package is your 9€ one? The root server start at 13€ - maybe they price hiked already? Netcups vServers aren't really comparable to the CCX13 of Hetzner, as they have no guaranteed resources - those will be the root server on Netcups side.