Hi,
I wouldn't say that Kingsford is "wonderful", just that it works well for me, and I guess for lots of other folks, too. It's readily available all year around where I live; it's inexpensive, especially when I stock up on it at the wholesale warehouse store during BBQ season at $10.95/48lbs; and it burns hot in a very predictable way, providing long, consistent heat. It's so predictable that I know exactly how much to measure out into my charcoal chimney to cook certain foods, and I know I won't have to add anymore fuel part way through the cooking process. I like hassle-free cooking, and Kingsford provides that.
There's certainly nothing wrong with using lump charcoal in the WSM, especially if you have abundant access to it at an affordable price, which I don't have where I live. I have to travel a long distance to find it, or pay inflated prices at a BBQ specialty store, or buy it mail order and pay more in shipping than for the charcoal itself!
I would encourage you to conduct a test to see which you like best from a performance standpoint, then share your results here. Cook one brisket using lump charcoal and another using Kingsford, then compare notes. Did one light easier than the other? Did one last longer than the other? Did one taste different from the other? What was the difference in cost, ease of acquisition, etc? You can also weigh factors like whether you prefer a more "natural" product like lump vs. a more "engineered" product like Kingsford. After all that, you can make a well-informed decision about what product is best for you.
Regarding the ingredients in Kingsford, see this post:
http://tvwbb.101inc.com/tvwbubb/Forum4/HTML/000112.html
Regards,
Chris