I took their training two years ago and had a great time and learned a lot. Detail King's training focuses on two parts: the business aspect of starting a detailing business on day 1 and how to use the equipment and products on day 2. The downside is if the class has a large attendance, you may not get as much hands-on time in the shop as you might like. The upside is if you don't have much background in running a business, they will help you with your business plan and how to deal with problems you will encounter as a detailer.
As far as their products go, I like many of their products especially their Blue Diamond polish-sealant, but I still have a selection of other brands, such as Meguiar's, Blackfire and Gloss-It.
If you're wondering if you should go, I highly recommend it. At a later time, spending a weekend with Mike Phillips at AG's garage would give you a well-rounded education as Mike's classes focus almost exclusively on tools and materials.
A third alternative is to schedule a week in Big Bear Lake CA with Renny Doyle, "Jedi Master" of detailing. He works one-on-one so as you'd expect, his classes are expensive but the training is top-notch.