[iakov]

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.

[sandreas]

I don't think that LEGO is better. They also have slightly off color, non fitting parts. Especially the "glass" parts are worse than Cada or BlueBrixx, but I'm not trying to convince anyone.

I think that everyone can pick whatever liked. However, the term "fake LEGO" is a bit weird, because the other manufacturers also have well designed parts LEGO does not provide...