EISCO High Resolution Quantitative Spectroscope, 400-700 nm, +/-5nm

It works. Fascinating differences between spectra of 'white' artificial lights. Crudely made: needs a finer intake slit, less internal reflection and a lens to view through. But you can actually read off the Angstrom wavelengths, more or less. Feasible to fix these things yourself - a bit of extra science!

It's OK for a toy. But the slit has to be a bit narrower to be able to see 5nm separation!

Out of focus . Useless.