innerwise Shop GmbH
This app works just fine and exactly for the purposes described. You have to be careful though if you are handling products with different VATs inside one country (eg. VAT in Germany: 19% normal; 7% deducted) which does not work with that app solution....
Exemptify just checks if the VAT-ID exists.
In Germany the law says that the verification has to be done "with the diligence of a prudent businessman". Many sources on the web as well as our tax advisor state that only the "qualified validation" which also verifies the address meets this requirement. Consequently in case of an audit any merchant just checking the existence of the VAT-ID likely will have to pay VAT for any purchases with a (valid) VAT grabbed from the net where the address does not match the buyer's.
I'd happily update this review if anything I stated is not accurate.