This error appears due to the Gatekeeper security feature included with OS X 10.8 (Mountain Lion) and later.
To bypass this, open System Preferences and click Security & Privacy. Change "Allow apps downloaded from" to Anywhere.
Once done, try running the installer again.
If you prefer to keep Gatekeeper on, you can always revert this setting to default after installing your iZotope product.
*For newer operating systems (OS X 10.13 and up), the app you're installing will appear under the "Allow apps downloaded from" menu. Click "Open Anyway" next to this and your software installer will launch.