Because I paid for it.. am still .. mostly 'cause I spaced the renewal.. but it's easy to use, as a tab hoarder + use 2-5 other browsers.. all with 100's of tabs over 5-20 windows.. I have pics of my gradually growing # on the 'Tabs Outliner' plugin.. like 600 was top..mania.. heh.. Anywa...

Their Dev team mess up with users data. I was a paid user and they forced us to adoped changes that users were disagreeing in their forum. They also never replied our emails.

Very affordable for premium features and I've got thousands of bookmarks saved up in Diigo.

It (the paid version only?) has a cool feature that allows links to be arranged and exported in a clickable outliner form. It can be edited, reformatted, etc. To me, it made it more universally useful, if I wanted to share the links, or use them in Word, etc.