I suggest to first watch Ranking King online (YouTube) with subtitles to fully understand the dialogue, because there are only Japanese subtitles for the DVD, and to watch what was originally aired. I noticed some non-Infinite background music has been removed (ex. in the Strength King episode, "Gee" and "You Raised Me Up" were both removed). For the most part, the DVD version appears to be the same as the broadcasted version. Watching the DVD version is still just as enjoyable to me, if not better because the different episodes aren't as confusing and flow better. Also watching without subtitles is manageable because so many tasks are physical rather than mental or verbal, and without subtitles allows you to focus on Infinite more rather than keeping up with reading subtitles.
Overall, the Ranking King DVD is one of my most favorite Infinite items ever! I can always watch the episodes over and over again, gawk over the photobook and admire my precious Sungyeol shirt. While it does cost more than most other Infinite products (this is roughly $100 USD), it is a very special piece in anyone's collection.