Pros
The people at WhatCounts are probably its greatest "pro" in my book. Everyone I've worked with--or for--in my 6+ years has been kind, smart, focused, and hard-working. The other thing I like is that WhatCounts is never satisfied with status quo; they are always looking for impactful ways to improve the product and make work fun.
Kontras
As with any dynamic company there are changes that require flexibility in attitude and sometimes in job duties. For a person who is not comfortable with change this would be a "con".