You mostly pay for added features. In some programs, the free version does not include email scanning. Or the support for the product may be limited. Pay versions will include both.
One way to find out what pro vs. free differences are is to use the side-by-side charts most of them have. Then make your decision based on what you feel it's important to have.
IF you decide to go with a paid version, see if it has a free trial. Install it, use it. Is it user friendly?
User interface simple and easy to navigate? How often is it updated? Does it have any negative impact on your system? It won't take long to find out if it's something you want to purchase. If it is, wait until the trial period is almost up. A lot of times, you will be able to purchase it at a discounted price.
Edited by Queen-Evie, 04 December 2008 - 11:52 AM.