Tell me what's so great about synthetic brushes.

[shave/brush]

I was thinking about one of the XL's or maybe one of the black fiber ones. What is so different about them?

I own a Muhle Silvertip Fiber XL and I also own the Plisson plus several other synthetic brushes. The Muhle STF XL is my favorite by far. It is a 25 mm knot but it feels much bigger.