The Personal version has limits on certain functions and the Premium version has none. However, when it comes to deciding which you should purchase for your application, consider the License Agreement as well.

	Personal	Premium
Read/Write ATOM 0.3 Feeds
ATOM Feed Auto-Discovery
Advanced ATOM Discovery
Support for ATOM 1.0
Convert between ATOM 1.0 and 0.3
Refresh Feed Function
Exception Logging Support
Pingback Support
Trackback Support
XML-RPC library Included
DB Helper Library Included
UniversalDateTime Class
Captcha Controlled User-Input
API/Namespace Documentation
VB and C# Snippet Support