Empirical evidence. I've tried some fake brick sets, most of them were obviously not as good. The QC is worse for sure, but it's the little things - sometimes it's weight, sometimes it's texture, sometimes it's color that is slightly "off".

Those "other bricks" are quite useful when you want something that Lego won't produce. For example gimp figurine for your Pulp Fiction diorama.

Well, simple: we have some