This release contains two things: You can now fetch timings using multiple browsers for one run and (hopefully) all errors that can happen are logged to the error.log. The last one will make it easier to report issues and fix them.
The parameters for fetching timing metrics through the browser have changed; use the c parameter to choose browser and z how many runs per page. It looks like this now (analyze http://www.sitespeed.io fetch timings using Chrome and test each page ten times):
bin/sitespeed.io -u http://www.sitespeed.io -c chrome -z 10
Or fetching using both Chrome & Firefox:
bin/sitespeed.io -u http://www.sitespeed.io -c chrome,firefox -z 10