I have a Z-plus insert as well which is awesome, it's my edc lately along w a little Tsuge Drew Estate gadget. Works better than lighters many times the price. I have the soft flame pipe and single jet torch one as well. The pipe insert came in a hearth and home "Fippo" if you will for less than the insert alone on sale from a fine store in Bethlehem, PA that will remain nameless.
The thunderbird I believe is a different product made by Vector, a company whos lighters have given me endless problems. Mb bad luck idk.
Lastly, recently I picked up a butane bleeding tool with a vent which actually works better than a screwdriver or pen. The gas needs to be completely drained before filling to achieve maximum fill. I find the capacity of the z plus large even using a few times a day and the whole thing is clear so its very easy to slide it out and see the level.
As for the soot which still seems to form even w the butane, but not to the extent of naptha, every So often I use an alchohol prep on it and it looks like new.
I like the classic insert alot but the naptha hurts my throat and the taste certinly doesn't enhance the tobacco. Really I prefer hemp wick or matches altogether but theyre a pain outside where I ussualy smoke.