I looked at various parts of the video. In one part he is saying that a sandbag should be added, but he just holds it up, he doesn't say where it should go and in fact there is nowhere for it to go - which means that it can only go on the base of the stand, where it can't counterbalance the weight on the boom...
The whole point of a boom arm is that it needs to be part of a heavy duty stand that has a large footprint and it needs to be perfectly balanced, in other words the counterbalance needs to be adjusted so that the flash head doesn't move even when the clamp that locks the boom in place is left completely loose - it is then balanced and reasonably safe. If the stand isn't strong enough or if the weight can't be counterbalanced, there is a good chance IMO that someone will end up wearing a heavy flash head.
On the section with the grip, there is no counterbalance of any kind, making it patently unsafe for anything that actually weighs something. He does mention that it should only be used for something that isn't heavy, but he doesn't stress that point. He uses that arrangement with a very lightweight continuous light, for which it might be reasonably OK, but if that was all that I had I wouldn't put any kind of flash head onto it.