Well, it's not - that's why they include an achromatic lens element to reduce color fringing as well as an (optional) rectifying eyepiece. Microscope eyepiece cams aren't too pricey on eBay and might deliver better results than a consumer cam.

I can see a lot of cool little science fair projects with something like this, not all for astronomy either, eg mount 2 of them in parallel and build a stereoscopic analysis tool.