Why is it ill advised to eat the solid aspirine formed from salicylic acid + acetic anhydride
Unless you worked to Pharma industry Good Manufacturing Practice you shouldn't trust your product

The simple reason why you should not trust the product is that that you don't know it is safe unless you have followed rigorous quality control processes. The drug industry follows carefully regulated quality-control processes known, in Europe, as Good Manufacturing Practice. This is far from easy to meet and even major drug firms sometimes have their factories closed because they fail to ensure it.

For your particular reaction there are many possible things you would need to check before knowing the product was safe to consume. You really don't want to guess whether all the acetic anhydride or acetic acid has been removed: even a small amount will be bad for you (you can't rely on intuition that it should all have been removed). And are you sure there are no nasty side products? Have you checked? Have you checked the purity to make sure? Have you had a check by an independent party?

If you can't say yes to all of these (and more: go read the GMP standards for aspirin manufacture), don't take the product.