A: I didn't try TabExtend, but it looks like a nice product. It takes a different approach to organizing your resources. I think it comes down to personal preference.

Beyond the basics (low-friction access and creation of bookmarks), a good bookmark manager should make it easy to contextualize and rediscover information. That's what we focus on. Our tagging system is the first step in this direction.

If you would like to try BookmarkManager.com, you can play with our interactive demo (no sign-up required):
https://bookmarkmanager.com/demo

If you want to learn more about our tagging system, you can read this:
https://bookmarkmanager.com/tagging#inclusive-vs-exclusive-tagging

I hope this helps. Let me know if you have more questions.