My short experience with Barmer was extremely frustrating. I only worked in Germany for two months before moving back abroad, and during that time they showed a surprising level of incompetence. They repeatedly wrote my date of birth incorrectly, despite being given the correct details, and sent important letters to my employer’s address instead of my home address — even though I had clearly communicated this.
If I had stayed longer in Germany, I would not have trusted Barmer with my health insurance. Based on my experience, I cannot recommend them.