Erm, wouldn't it be cheaper to simply put a real person in it? After all, the testing in a chemical environment doesn't mean it has to be toxic or lethal
It might be cheaper, but less effective. This gives a constant standard across years of trials that human subjects could not. It can be fitted with sensors that enable it to be used in a real environment that you couldn't expose a human to. Lots of other reasons but mostly about better rather than cheaper.