The ET-S has a good quality Pyrex glass tank that is a good choice for Ego sized e-cigs.  
The pyrex tank helps to intensify flavour compared to other polycarbonate clearomizers, as well as being more robust!

The Aspire ET-S is known as a bottom dual coil and is a good step up from the normal clearomizers with more vapour production, thus giving more flavour with increased vapour production and more hit!

To fill, turn upside down, unscrew the base with the coil attached, then pour the e-liquid down the inside wall and avoiding the central air column. Dab excess e-liquid off the coil with a piece of tissue before re-attaching the base plate. Always check the coil is finger tight inside the base plate before assembly.

Allow the unit to stand upright for a couple of minutes when using new coils, to all the e-liquid to thoroughly soak the coil.  

Coil life is on average 1-4 weeks, but this depends on usage