Hmm, unfortunately there seems to be a small but annoying bug - if you start with clean NHM (without config) then the entered Bitcoin address is not stored in config.json and therefore not used in the benchmark. We'll release a bugfix soon, meanwhile just "Start" miner for a few moments (will start mining on first algo - X11), then Stop miner, close NHM. Then start NHM again and you should be able to run benchmark.