We had a few days stopover in 2012. Slightly eastern block feel to some of the towns (the wall ran through that area) but probably the most techy mtb potential of anywhere we’ve tried in Germany. Will definitely be going back to investigate properly sometime (have previously tried and been underwhelmed by Black Forest and Pfalzerwald).
Didn’t manage anything too interesting as only had 2 days and one kid sick plus a mate from Kassel managed to properly break himself a few weeks before (so no local guide).
There was a keen mtb couple staying in our b&b. He had lots of rocky singletrack on his “navi” and was really positive – reckoned singletrack / cheeky trail mix of walkers and bikers got on fine in that region with far fewer conflicts than the south.