The iStick 20w can read 1.0 to 3.0 ohm coils.
The iStick 30w can read 0.4 to 5.0 ohm coils.
The iStick 20w will not read the .8 coil.
Keep in mind coils are not always as stated. For example, a 1.8 coil may be anywhere from 1.7 to 2.0. It is just the nature of pre-made coils. If you want coils at a specific ohm you will need to build them yourself.
The ohm reader on the iStick 20w is accurate.
Devices such as the iStick 20w and Genitank are not designed for cloud chasing, lower ohms or high wattage. They are not sub-ohm devices. Sub-ohm is anything below 1.0 ohm. There is a learning curve to sub-ohm use and battery safety. That is the territory where batteries can and do explode.
I suggest you spend time with the iStick 20w and Genitank. Use them as designed to learn how they work and the basics of vaping hardware. Learn the max volts/watts that work with which juices, your comfort range, etc. Then, upgrade if you want, at some time in the future.
If you do not already know them learn the problem areas of the iStick 20w. Be gentle with the 510 connection because the threads and pin are brass which is soft and can be damaged. Do not screw a 510 device all the way down. I leave a space,the thickness of 2 business cards, between the bottom of the atomizer and the top of the iStick. If you use the 510/ego adapter that came with the device you will have no problems. If you connect a 510 atomizer directly to the IStick just be gentle. At any sign that is is not threading smoothly stop, then start again. Also, be cautious with the USB connection. Don't attempt to force the charger connection into the iStick. Be aware that the iStick 20w uses mean instead of RMS to read the volts/watts. This results in the device running hotter than shown on the display. 3.0 volts on the display is actually closer to 4.1 volts. It levels out as the temp increases. Don't be concerned about what is on the screen. Adjust it to your comfort and best taste level.
I have several iStick 20w devices. Love 'em. They just require a bit of forethought and a gentle touch. And they are darn good lookin'.
Enjoy!
Eleaf iStick
ECF iStick Thread:
http://www.e-cigarette-forum.com/forum/variable-voltage-apv-discussion/601111-eleaf-istick.html
~ Elaine