The blog post is poor. It has TailScale's "house style" of folksy reminiscence and Avery's stream-of-consciousness writing stylewrapped around an announcement. It only says two things, one at the top, and one at the bottom: "We raised a $100m for our war chest; we don't have any plans for how to use it besides extending runway for our current operations". The middle is left trying to justify why that is a good thing, despite not having a reason beyond "we know a lot of rich people who know we are wicked smart and talented, so they want a piece of equity in us".
The home page is a pretty clear exposition of what TailScale is: https://tailscale.com/