For as long as Kurzgesagt has been around, they've always been a favorite of mine. The art style, well-researched topics and cited articles, and corrections when needed have been a pretty nice change of pace given standard YouTube fare nowadays.
my brother happened to be cited in this video, he had nothing but positive.. nay, a glowing review of their performance.
as you also indicated, my brother mentioned that they seem to go above and beyond not just with the beautiful format, but in researching even deeper into the core material to make the video as accurate as possible.
I actually bought their Immune System book, just cause I've enjoyed their stuff for so long. I remember those stupid little birds over a decade ago, and the book serves a little more purpose than their general merch. It's also really well illustrated. Haven't had the time to read it yet, as it's pretty lengthy and sorta dry as a "scientific" immune system picture book should sorta be, lol.
Also, awesome your brother got referenced! That's pretty sweet