It doesn't seem to have a time cut, so that makes it easier than Pendle in that regard. It can't compare to TCR. It's more like MdS or Transpyrenees but with smaller climbs. I've ridden a bit in Germany (TCR and touring), I mainly want to ride in the Vosges.
I'm sure it's hilly but it's not going to be harder than Pendle, TCR parcours, Alps, Pyrenees, etc.
I've ridden in the black forest and it was certainly hilly but I wouldn't say it was the hardest thing I've ever done.