Being just a bit shorter than the iPhone 5s and featuring a top-filled system to make spillage far less likely, the Aspire PockeX is a very good choice for a compact all in one.

The PockeX is actually a sub-ohm device, using a 0.6ohm stainless steel Nautilus X U-Tech coil (available here).
The atomizer actually screws into the top cap instead of tank bottom. This allows you to replace the atomizer without draining the liquid from your tank. Very handy!

Other features include a wide drip-tip and large top-airflow for increased vapor production. The tank has a 2ml liquid capacity, meaning this baby is fully TPD compliant and the battery has a 1500mah capacity.

The complete unit measures 117mm x 197mm, making it one of the most compact sub ohm pocket all in ones around. It's size and functionality make it a very good choice for a step into sub ohm vaping.

This set includes:
1x PockeX with a 0.6Ω Atomizer Pre-installed
1x Replacement Atomizer
1x Micro-USB Charge Cable
1x User Manual and Warranty Card

Should you wish to purchase as a bundle with extra coils, please take a look on the Aspire Starter Kits & Bundles page.