The ability to create, test and share multiple versions of pages. Easy to use interface with an active community that supports you along your journey through optimizing webpages. Some features are not user friendly (like adding tags). This can be resolved by training some one at their office how they work etc., but this isn't always possible depending upon where you're working from. I think it's worth trying out if you have been looking for something similar without finding what you were searching for. We've had success in improving our SEO performance by using different variations of landing page copy to reach customers. There has also been increased traffic which translates into more sales overall.