From SkillCult's the video:

"Bulgarian giant has a good combination of attributes for the home garden. It is self blanching, so there is little if any washing involved. It is large. And, it is tasty! It's one downfall is perhaps that it is not super hardy. I've been selecting against winter damage for some years now, but it would have to be grown through the winter with protection in very cold climates. It will still make a good summer leek though and better than most for the same reasons listed above."

He has the seeds for sale at his online store.