I personally, with a lot of testing (over 25 different juice delivery products), came to the conclusion that I was sensitive to the wire that Kanger uses.
I tried removing the flavor wicks, flipping the gaskets, using both the thinnest and thickest juices on the market (with direct confirmation from vendor testing, general public opinion, and various viscosity tests, tested by dripping each juice onto free hand silica to measure the speed of absorption before vaping - as well as priming the Kanger wicks before vaping) also, testing using airflow controllers, various trip tips, and various tank fill amounts.
Nothing would prevent a "metallic/extremely harsh/somewhat smokey" hit. I believe this type of flavor is sourced from material on the wiring itself, and that either the contaminants can variate between builds, or that some people are sensitive to the particular alloys - for me, I don't seem sensitive in the least to certain types of NiChrome, though it could still have depended on the particular vendor's willingness to torch/clean their own NiChrome.
However, I recently tried the Kanger Evods, which seem to wick better than the Protank II, at any rate, I could taste more of the juices being used than I could in the Protank. Yet, despite that, there were still metallic and smokey layers - even to juices like cheesecake, mint, and blueberry. All samples provided by a vendor, who was also an expert RDA builder, who filled them himself.
The same vendor told me personally that his particular taste buds also taste a concerning taste on most any device but his RDA's, and trying his build, I agreed perfectly - despite the Evod's being "okay", the difference from them and a clean mod was night and day. No metal tastes. No smokiness. I didn't have to tilt his mod or do twenty manipulations just to get a good flavor out of his. That same concept should apply to every device being marketed as easy to fill and easy to vape.
And, I believe, to people who aren't sensitive to these devices, that the devices tend to taste wonderful. There are plenty on this forum who describe these tanks as though they were RDA's in terms of flavor, and yet everyone is taking out flavor wicks equally and not getting the same result, and some aren't ever fixing the issue. I was stuck in the "it's the company's fault" mindset for the longest time, but with applying some discoveries on my end, I now think that a coil sensitivity may be more widespread than some of us may think.
If you do think you have a sensitivity, do not fret - plenty of vendors wrap their own coils using various types of Kanthal and NiChrome, some torching and firing the wire before selling it to ensure maximum performance and taste. These pre-wrapped coils attach to a an RDA almost easier than installing a Protank head, and the only extra steps required for a bit of safety is using an ohm checker (as one really should on any head or clearo device.) They also can be cleaned tremendously easier than replaceble heads.
There are a lot of easy alternatives in today's vaping world, and my big advice is to not keep spending money on items that simply don't work for you. If one doesn't work for you, chances are, another device, wrapped with the same wire and using generally the same wicking mechanics, will not work for you either. There's very little difference, in terms of physics, from Evods, Protanks, CE4's, iClears, virtually anything else. The only difference is you vape CE4's generally upside down, where you vape bottom-fed tanks pointing down. Both should work equally as well given that technique.
