The 1.x versions of the module uses hook_exit() to run cron at the end of the page request after the page has been sent to the browser, but has problems dealing with page caching. The 2.x version does not have this problem.
The 2.x version no longer has its own module page at admin/settings/poormanscron. You will find the 'Automatic cron' poormanscron setting at admin/settings/site-information at the bottom of the page. This is the same location of the automatic cron core feature of Drupal 7, so get used to it now.