While relatively new to SEO, I've tried a few SEO tools and I have to say Squirrly has been the only one that has made me feel like I know what I'm doing. It helps me identify what needs attention, suggests what to do and I can see and appreciate the results from those changes. I have ben able to rank my site better organically since using Squirrly - something I struggled with before.
I've not had a chance to use all the functionalities in the tool as it is quite comprehensive but, So far so good.