They made a great single fish in my experience. They are timid for Mbuna, but they are pretty bold fish overall. I'd expect them to hide for the first few weeks, but I'd be surprised if it wasn't out in the open after settling in. Yellow labs were frequently one of the ones I had to pull out for being bullied in my community, and they seemed quite comfortable and active when kept alone in 20 gallon quarantine tanks. Pretty much impossible to gauge fish "happiness" but they would move gravel, pace the glass, and beg for food when I'd walk by which is as good as I could expect.