I tried the burger once - it's light years beyond "veggie burgers" of the past, the taste, look and texture is very similar to the real thing. I wouldn't mind if you told me I had to give up ground beef and eat these instead.
$4bn sounds pretty high, but I can see the company being worth a lot. Aside from health and ethics concerns, it's becoming an environmentalist thing to reduce meat consumption due to the enormous quantities of water and other resources that livestock consume, and the CO2 they emit. That said, I'm not sure how easy or hard it would be for competitors to replicate the product.