Last alert bulletin we got for our FEM specifically states:
The e-cigarette is an atomizing electronic device which has similar functions to an ordinary cigarette. It contains a nicotine cartridge and a smart chip lithium battery.
They may be brought onboard, but should be securely stowed and may not be used at any time.
It's also listed in the items (PED's) that are prohibited from use any time onboard the airplane.