The WhatsApp Business app is for external business communications, whereas the WhatsApp Messenger app is for personal communications. We've worked to make each app GDPR-compliant based on its intended purpose. If you're a small-to-medium sized business, you should use the WhatsApp Business app for business communications with your customers. The WhatsApp Business app is free to download from the Google Play store.
For more information on GDPR and managing contacts in your device address book, please see this article.