Among people who preferred one space, reading speed was about 5 wpm higher with one space. Among people who preferred two spaces, reading speed was about 9 wpm higher with two spaces. In other words, people preferred whatever they preferred, and the difference wasn’t very much anyway.
This is a great break down of the bad science reporting in the recent “2 spaces” articles. A lot of science reporting in popular media is done without looking at the study in question in detail. The mother jones article breaks down why this was really weird.
But, the original article did demonstration one thing well. We all have a tendency to broadcast information that confirms our biases, without looking deeply as to whether that was properly grounded. Which is why a poorly done study on a trivial but polarized issue generates a lot internet traffic.