I tell my students that they should know them almost as fast as their multiplication facts. The ones who succeed always do well with the remainder of trigonometry.
When teaching the unit circle I always begin with special right triangles, but once that foundation is laid, I use this left hand trick. You can find the notes here.
This is SO much quicker than drawing tiny special right triangles for every problem.
Quick tip: I also emphasis that tangent (opposite/adjacent) is really just slope. Every student should know the slope of a vertical, horizontal and 45 degree lines, so they really know tangent of the quadrantal angles and all of the angles with a reference angle measurement of 45 degrees.
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