There are several things I don't like about the video, but I do like that he made a video about being safe.
First, Everyone needs to be aware that you can't just go buy rope off the shelf at the hardware store. It is not made to handle the forces of a fall. You need a rope that is rated for climbing, and built to withstand abrasion and the weather. the stuff you go and buy from Lowes or Home Depot isn't going to cut it, and you shouldn't risk your life on it.
Second, If you are running a static line and a prusik cord, you need to understand that the prusik cord needs to be between 60-80 percent of the diameter of the static line to get a good bite.
Third, I wouldn't trust my life to an overhand knot. It will probably hold, but why risk your life on a "probably." Instead tie a figure eight on the end of the main line.
On the prusik, there were two things. first, I wouldn't tie an overhand knot here either. I would go with a double fisherman knot, with safety's tied on both ends. Once you wrap your prusik around the main line, you don't want your carabiner hanging from the knot, so rotate it out of the apex of the prusik loop.
The intention of the video is great, and I don't fault the guy one bit. He just left out a few important details.
My honest suggestion would be if you don't fully understand ropes and knots, to spend the money and buy the pre-made sets. You're not gonna save much money anyway if you make on your own and make them right anyway.
