Read their descriptions CAREFULLY to determine if something is the "brand" or not.
If it doesn't say "Kanger" it isn't. If it says "Innokin" or "Liqua" then most of us think it IS.
Then, for the knock-offs, maybe look here for people who've tried it.
I've seen several people here indicate that they're very happy with the EVOD's they got from FastTech - mine should be waiting for me today in the mailbox