There are some next-prev post plugins that are floating around the free wordpress repository. So why bother with this excellent premium plugin? Glad you asked.
Amazing support is all the reason you need to know. Wordpress updates, theme updates, and misc 3rd party plugin updates can break our most favorite plugins at the drop of a hat. Unless each of us are CSS/jQuery/PHP experts, I strongly suggest going with QuanticaLabs and save on the heartburn. Now you won't need to hold back tears as you disable a free wordpress plugin which breaks due to updates.