Playing as a guest won't appease what appears to be the major issue, that is showing the time you spent on the puzzle against the bell curve of previous solves. That still occurs. You just won't accumulate points for the game, which it also reminds you every puzzle you solve.
People who truly don't care about how long it takes to do the puzzle, they only play for the fun, would not care about the bell curve statistical graph. If you didn't care, you wouldn't even look at it, but just click a button to move on to the next game or exit.
Only a person who cares would be upset by the graph.