As long as you are following the licensing agreement below then you would only need to purchase BPS Pro once for all of your personal or customer/client websites.
BulletProof Security Pro Licensing Info:
BulletProof Security Pro Software License
The BulletProof Security Pro license does not have a limitation on the number of websites, website domains and website hosting accounts that you can install BulletProof Security Pro on, as long as these websites, website domains and website hosting accounts are either owned directly by you, supported directly by you or managed directly by you on an ongoing basis. Please read the BulletProof Security Pro Software License before purchasing BulletProof Security Pro.