Are there any superior alternatives at a comparable price? Does anyone have firsthand experience with this sensor? In particular, would detection below 450nm be possible with decreased resolution/accuracy?
Well, it is a wavelength sensor, so it can measure the wavelength of a laser in the 450-950 nm range. This requires calculating the ratio between responses of the two photodiodes stacked in this device, and then using a lookup table to find the corresponding wavelength. This could be accomplished with 2 accurate ADC's and a microcontrontroller.
To make it accurate you'd need tabulated response data instead of the 2 graphs in the datasheet.
Extending the range beyond 450 nm doesnt seem feasilbe though: the response of photodiode A is virtually flat, and near zero, in that range, so the ratio between A and B is not affected by wavelength anymore. This also holds true for IR light beyond 950 nm or so.