The main difference between a shisha pen and an e-cigarette is that an e-cigarette is designed to deliver a kick of nicotine to tobacco smokers, where as a shisha pen is designed as an easy to use flavoured enjoyment - without nicotine.
E-cigarettes are used to replace tobacco cigarettes and are thus under constant use. This means that an e-cigarette must be maintained, with parts needing replacing and nicotine e-liquids needing refilling. Conversely, a shisha pen is designed to be used for recreational purposes and in social situations. As they are not under constant use the same way that an e-cigarette is, there is no need to worry about replacement parts etc. A shisha pen is completely disposable, and once it has run out of juice, it can be thrown away.
Also, the disposable nature of an e-hookah combined with the lack of nicotine means they are much cheaper than e-cigarettes – furthering their function as an enjoyable social tool rather than one to control a nicotine kick.
Another difference between shisha pens and e-cigarettes is in the way that they function. Due to the non-disposable nature of the e-cigarette, there are many varying designs out there, using different set ups and designs. However, most e-cigarettes require a button to activate. This button temporarily activates the heating element and vaporises the nicotine e-liquid. Many shisha pens are activated through suction, and do not require a button.