I suffered the same as everyone else with the standard who's online module that comes with Joomla. Then I purchased this one and kazam - accurate who's online figures with a really neat display. I also found the company to have impeccable support.
I got this extension, and it did not install correctly for the first time. Its very basic, there are no additional features like members signed in, or state when the maximum number of visitors to the site.
Although it achieves what it states but the price is very steep, I think there are other extensions (commercial and non-commercial) deliver a lot more.