For PG/VG based extractions, high levels of filtration help but only to an extent. They're still pretty gunky when compared to synthetics. Even when filtered at 1 micron, I re-wick/dry burn after every tankful (3-4ml). I've experimented with many methods in an attempt to achieve better performance but so far none have panned out.
PGA (ethanol), based extractions are cleaner. In addition to filtration, you can precipitate the oil, wax and resin out of an ethanol extraction (
freezing process), making the cleanest best performing NETs I've encountered so far. I vape flavored NET (caramel, vanilla, crème, nut and or other flavorings added), and re-wick/dry burn every 12-16mls. The coils don't appear much worse than if
vaping a straight synthetic like Ahlusion's Caramel Wild Wood. Performance and flavor are why ethanol is my current solvent of choice when it comes to tobacco extraction. It's pricy and requires additions steps/procedures but for me it's well worth the cost and effort.