So far so good, they last as long as any other tips I've bought. I am of the opinion that soldering tips can only be used for a certain amount of time, even if they are cared for with tinning, cleaning, etc.
The 3mm chisel tip is a good choice for terminating old vacuum tubes. Allows you to increase the surface area for heat transfer. These tips are perfectly shaped and easy to tin. My first tip was enough for several repairs and restorations with the usual maintenance cleaning and re-preservation between uses. Reducing the temperature between each use also increases tip life.