Hi Will,
Thank you for reaching out to us! The Joyetech AIO is not variable voltage or variable wattage, but it is a regulated device. It offers dual circuit protection, which safeguards against over-charge, over-current, and over-discharge.
The different resistances will result in different styles of vaping, and they are all compatible with the AIO. The 0.6 ohm coil that comes with the AIO will produce warm, thick vapor, but it has the restriction of a mouth-to-lung vape; the 0.5 ohm coil will produce similar vapor, but has more airflow, so it's in the style of a direct-lung vape; the 1.0 ohm coil will have a similar draw to the 0.6 ohm coil, but it will produce a cooler vape with less vapor production; and, the 1.5 ohm coil will have the tightest draw with the coolest and least amount of vapor.
Best regards,
Brad