I'm using both their dedicated servers and the cloud offering and never had any issues. Speed and latency are consistent both within Europe as well as to the US (not monitoring much traffic to Asia). Latency from their DCs in Germany to Frankfurt is around 3ms, so comparable to the central Europe offerings of most cloud providers.
I haven't noticed any downtime either -- all my downtime has been my own doing -- I only run a few small sites and periodically staging versions of client applications so I don't have a crazy amount of load.
I've been using Hetzner for roughly 2 years and am a pretty happy customer.
I can say though that the latency is pretty bad when compared to local options -- their server are pretty geographically far from where I and others who use some of my apps access from, and I get ~200ms of latency that I can't do much about. I've looked a traceroute and it's not their network but rather some points in between.
In the past two years, I remember they have done scheduled infrastructure maintenance twice and unscheduled interruption for a few hours. So, no, it's not 100%. But, AWS has also had some interruptions. From personal experience, this Hetzner downtime has simply been negligible enough. Bigger issue have been replacing commodity memory a few times, which could have been avoided by paying a few more dollars for more quality.