Absolutely nothing wrong with running ultra sub ohm, as long as you keep it safe.
.04, TO ME, just sounds too close to the edge for comfort. All that needs to happen is for the coil(s) to shift every so slightly in the wrong direction, and the connection changes, and bam, dead short.
Besides, If cloud size is the ONLY goal, coil ohm-age isn't the determining factor. Airflow plays a HUGE roll. Now, if we're trying to get both clouds and flavor, thats a different story. But if cloud size is the only goal, you dont NEED to go ultra low. Get the airflow right on a well built 1ohm coil, and you'd be very surprised what kind of clouds you can make.