It is a sample book with all the colour filters that Lee produces. These filters are usually used for theater lighting, in front of a spotlight.
Use for flashlights is limited, you can create and alter tints with them, at the cost of light output. The sample filters in this book are large enough for most smaller flashlights. For me it is a nice thing to have, but I will probably not use it much for anything.
Got the Lee filter samples from Valor today. Tried it with a diffused Xiaomi USB light, that has a greenish tint (gets worse with higher output modes). Measured on the highest of the five modes.
The diffusing filters (a lot of different kinds) also seem very cool.
Three different minus green filters tested: minus eighth, quarter and half.
Light loss
No filter: 100 %
1/8: 88.8 %
1/4: 83.8 %
1/2: 73.7 %
Color temperature shifts a bit lower with the filters. Here’s the CRI data.
I can recommend the i1Display Pro and the free Argyll commandline software. I use those two to do my runtime graphs. The spotread program bundled in the Argyll package gives you the color temperature and xy-coordinates for tint, but you would need a spectrophotometer for CRI data and spectral distribution. Don’t have experience with the ColorMunki, but it looks simliar to the i1Display Pro, which is not that much more expensive.