I haven't used factory coils in 4 or 5 years. I went to an RTA when Protank coils were lasting less than a day. At $8 per box of 5 they were getting expensive. The silver soldered legs were melting and opening up the current path. Eventually the Protank coil problem was fixed by wire welding the legs, but by that time I was enjoying my Kayfuns.
I have a vaping friend who says he gets about a month out of a TFV4 coil, so I guess the QC problem was solved by the technical departments of the manufacturers.
I'm still happy with coil winding and wicking with Koh Gen Do. It's a little more work, but the savings are still there. I replace a coil once a month or so and my wicks get replaced once or twice a week. I like fresh flavor.
I still have 2 or 3 boxes of Protank coils and Nautilus coils. I found them the other day in a storage box, along with a few boxes of SS mega LR cartos (2 ohm). I juiced up a carto and vaped for a while and went back to my Kayfun. Just me. Cartos weren't as good as I remembered.