I am trying to sell a fixed gear I built, and people have commented about a few things on it. First, someone said that a crank where the large chainwheel is part of the crank is dangerous. He said they are known for breaking off in the center. I am using the small removeable chainring anyway. Is this an issue?

Second, I secured the sprocket with a bb lockring. Someone said this is secure enough to use the pedals as brakes, and the rear brake should be left on. Is this true?

Thanks in advance