In the last few days, the er9 RD of a friend died for no reason. Got stuck in the hardest cog and nothing will make it shift, including reset, unplugging, replugging and everything i could think of. The FD works fine.
Then today, went for a ride with my gravel bike, and my own RD died exactly the same way! I went down a descent with bad asphalt and vibrations, at the end of the descent, dead RD.
I'm trying to get a response from l-twoo via the intermediary that sold me the groups, I'll keep you posted.
But as of right now, I'm extremely unhappy and would not recommend er9/erx because a bike has to work, if you can't trust your derailleur to shift, then buy something else.
I'll post updates.
TWO DEAD er9 RDs in one week under normal use.