I have used these for a while. There are pro's and con's to them.
Pro's: Hit really good.
If you break them in right, I can make them last for a couple of weeks. I rotate them around so that they darken evenly and try not to get the opening directly into the product. Sometime I don't even have to dip the tip, just heat it up and hit it. Keeps it cleaner by not over saturating the tip,.
Con's: Use them incorrectly and they'll clog and get loaded up, in a not to useful way.
I have found a way to revive them when I get them to clogged, and that's to drop them into some very hot water, and cook the clog into major softness. Then I either blow it out carefully with my mouth, or use a can of compressed air to carefully blow through it and free the clog. Another dip and another clearing, and the tip is good for another week. Eventually this does not work and the tip goes south electronically by a loose wire or short.
Overall, with careful management, I get a couple of months out of one pack. The quartz is my favorite. The open coils taste funny and I've never used the SCIV, so it the quartz tips for me all the way. I got my package in a few days after ordering, so was also very pleased with the costs associated.