Extensions ask more of a product than colour does. It has to hold an apex, flex with the natural nail instead of snapping off it, and stay light enough that a client forgets they are wearing it.

Builder gel or polygel?

Builder gel self-levels and suits technicians who work quickly in the lamp and want a smooth apex with minimal filing. Polygel does not run at all, which gives you unlimited working time to shape it, and is more forgiving if you are still building speed.

Structure is what lasts

Most breakages are a structure problem rather than a product problem. The apex belongs over the stress area, roughly a third back from the free edge, and the sidewalls need to stay parallel. A thin apex in the wrong place will fail whatever you build it from.