I've just watched it now - honestly, I don't think it's worth wasting your time on. It tells you nothing you won't already know about Seraphon, and they seemed pretty clueless on it anyway. If you want conversation and tips about our signature army, you're already in the right place. If you want my advice, don't bother.
I agree, at one point they talk about summoning and multiple of "7" to bring units in,it's "6" how bad is that, a couple of good tips on painting that's all.
It's the same attention to details typical of GW. The codex of the Space Wolves is out... and Bjorn the Fell-Handed is listed as generic HQ , instead of named character.