Do yourself a favor, stop listening to people that say you 'must' or it is 'better' to use nic salts in a Mtl style 'tank'.
It simply is not true.
Stop worrying about the resistance / Ω of the coil inside the replaceable head.
Resistance / Ω is a measure of impedance relating to the flow of electricity.
It is not a measure or description of an inhalation method - Dtl/Mtl.
The major difference between Dtl and Mtl replaceable atomizer coil heads is the inside diameter of the air pathway through the center of the coil that allows air to flow in through the air inlets into the air chamber in base, up through coil, into chimney/air tube to drip tip, and the size of the wicking holes in the body of the head.
You can see these, look down from on top at the head, the little hole in the center is where the air flow mixes with vapor & comes up through chimney & drip tip & what you inhale (larger diameter air hole = more air flow Dtl, smaller = less airflow Mtl). Look at the wicking hole size differences in the body of the head, (smaller Mtl, larger Dtl).
Always throughly prime new/unused heads before use.
With any replaceable head always start off at a low power setting (lower than recommended or printed on the body of the head) and gradually increase power taking a vape or three on each setting until you find the vape quality you want.
Your personal 'sweet spot'.
Stop worrying about the watts.
Stop trying to compare or relate a pod setup to mod & tank setup.
There just isn't an accurate comparison between the power & resistance used in different setups.
A pod setup and a mod & tank setup are entirely different methods of vaping. They are not comparable, 16w / .7Ω pod will not translate to 16w / .7Ω mod & tank setup.
The mod & tank setup up is much more efficient, much more adjustable to suit each individuals preferences, has consistent & accurate power regulation.
The whole point in owning & using a variable output power device/'mod' is to be able to raise or lower power going to the delivery device to find your own personal 'sweet spot' using an endless variety of delivery devices, resistance ranges, pg/vg ratio & flavorings.
How hot, warm, cool the vapor is, is dictated by your power & airflow settings.
Not enough of something gradually turn up the power, too hot, too harsh, slightly dry or burnt taste, turn it down.
Too little airflow open airflow control, too much airflow close down airflow. The airflow also acts as the coil's cooling system, more airflow = cooler, less airflow= warmer.
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Both the nautilus2 & the nautilus 2sS are fine Mtl 'tanks'.
I didn't have leaking problems from either, the occasional slight leak is common for any tank. Think about it, a liquid reservoir that has holes in the top and bottom, one to allow air in, one to allow airflow through, not uncommon to have an occasional seep or leak.
Aspire nautilus tanks use aspire nautilus BVC coil heads, aspire does make bvc heads that do not fit nautilus they are for other tanks/non nautilus. The box of heads will be labeled Nautilus.
I've always had very good longevity from nautilus 1.8Ω BVC heads, to the point I'd say the longest lasting of any Ive used to date.
But, I use clear, non sweet, 50/50 liquids between 10 -14w, and always start off new heads at 8.5w & gradually increase power over the first full tank of liquid.
By the time the first tank full is empty I am usually around 10w, during the second tank full I use anywhere between 10 - 14w depending on what I want/feel like, how cool or warm, slight adjustments in wattage also brings out different nuances in the taste / varies the flavor produced.
A 5 pack box lasts me a long time, 120ml ~ 140ish ml each head.
But, if you like sweet liquids or flavorings that are the goopy gunky type, or your liquids are colored or dark, you will not get anywhere near the head life.
When the nautilus came out I was still using 24 mg/ml nic in other 'tank' type delivery devices. I had to drop down to 18 mg/ml nic when using the nautilus. A more efficient delivery device than what I was using.
Over time I've reduced down to 3mg/ml, still using mostly Mtl tanks with resistances ranging from 1.8Ω to .5Ω.