I think this lesson needs to be titled differently, which I found a little disappointing. It isn't nearly comprehensive enough to be titled "all about" strings. It's what Justin gets asked about strings and his personal preferences and opinions on them. There is a lot more to say about guitar strings than is presented here. I appreciate his opinion but there is a lot more worth knowing or considering. Why not just recommend that beginners stay with the same string brand & gauge as the guitar came with from the factory? Most guitar brands will add string info in their product details.
The most notable omission is how he arrived at his preferred string choices. How many brands, gauges and types of steel did he trial to determine what was best for him? What is a good process for trialing strings? I'm a D'Addario fan myself, but that's because I tried Elixir, Adamas and a few others and developed a preference over time. I'm sure he has too, and it would have been helpful to hear what his experiences have been. Also, the D'Addario product line is massive and it's fun to try new strings. Frequent string changes and experimentation should be encouraged.
Lastly, I don't know when Justin had his band, but we are finding out now that as manufacturing has moved off-shore, the differences between name brands and affordable gear are not as wide as in the past. These off-name brands are frequently made on the same production lines and with the same materials as the name brands. We sometimes end up paying extra for distribution and advertising on the name brand, and don't see anything added to the product itself.