I love this extension. I use it a lot for capture whole page screenshots and sending them to OneNote for archival purposes.

The thing I like the most about it is that it takes multiple screen shots and stitches them together into a larger whole. This way, all of the captured screenshot is high resolution even if the original website spanned tens of pages that you had to scroll through in order to see.

Also, it has a nice feature for OneNote that will let you append to the currently opened page in OneNote so you don't have to select the page.

I guess they are some alternatives, but most them seemed pretty clunky in comparison and none of them to my knowledge captured a website that spans multiple pages at high resolution. If you take a lot of screenshots this extension is well worth the money to upgrade to the Pro version. Highly recommended.