Every clone tank I have ever bought was either unusable, used inferior metals, was usable but needed parts replaced to make work right, broke easily, leaked like crazy etc, etc, etc.
IMHO, it is far better to just save the money and buy an authentic tank.
I only buy clones of very high end RTAs or RDAs that are of good quality and I do my research before buying those.
you may find a clone of, say, a kanger subtank, but how do you know that the metal used won't leech crap into your eliquid (I do understand this can be the case even with authentics, though).
If you do buy a clone tank, I recommend tearing it down completely and boiling all metal parts for about 10 minutes before first use.