I used King for my IR written test. Their materials will adequately prepare you for the written test. But there are areas that are not covered. I think that will be true of any ground school. That is why I think it is important to stay active on this web site. I have learned a ton of stuff that has never come up in my formal training with my ground school and my instructors. I don't think it is a fault in the materials or my instructors. I think it is just a function of the fact that there is so much out there on to learn. As you may have heard before, your certificate is your "license to learn." That's very true.
In short, I don't think you can go wrong with the Kings videos. If you get the online version, you can download their videos on your Ipad or Iphone. When reviewing for the test, I loaded them on my Iphone and then played the sound through my car stereo on the way to and from the office. It worked pretty well.