There's very little use for a general purpose grating, since all commercial uses end up with custom gratings directly from manufacturers. So the ones that are sold in catalogs tend to be more expensive owing due to economies of scale, maintaining an inventory, and probably passing through one or more middlemen. And people willing to pay R&D prices to have something quickly drive up the price as well.
One of the reviews on that page mention implementing a spectrometer:
> The 1,000 lines/mm Diffraction Grating Plastic Film was used to make a high resolution optical spectrometer. First, the film was removed from its paper 2" x 2" card stock. The crystal clear film was next glued to an optical ring that was mounted in front of a very inexpensive 1,920 x 1,080 pixel webcam. The modified webcam was placed in the back oRead more about review stating Using the 1,000 line/mm Diffraction Grating in a Spectrometerf a pinhole camera-box and mounted at an incident-angle to the incoming light beam. In this configuration different light sources could be introduced to the new spectrometer and their light spectrum captured using a USB-computer input. Thus, a wide variety of light sources could be fully analyzed at a resolution of about +/- 2nm. Using this very inexpensive (1,000 lines/mm) grating, coupled with an equally inexpensive webcam, a high resolution optical spectrometer could be built for under $25.00
Most spectrometers use either reflection gratings, or holographic transmission gratings that are tailored for optimal efficiency to the wavelength range of interest, and also have exceptional flatness, surface quality, and so forth. "High resolution" is relative, and there are a lot of other figures of merit for spectrometers.
This is a prominent US supplier, and they offer a lot of useful info at their site:
With all that said, the plastic grating is a very cool thing, and with it you can demonstrate pretty much all the basics of gratings and spectrometers.
I'm no optical engineer, but I suspect one issue with those types of plastic gratings is ensuring the flatness of the surface; its just a thin sheet of plastic so I'd expect it to buckle/wave around quite significantly. More serious gratings are solid chunks of glass instead.
