FileMaker is a great Rapid Application Development platform and you get its benefits by using FileMaker Pro clients and FM Go. Additionally, it supports Custom Web Publishing via PHP, which is an nice extension of FileMaker. But using PHP to by the primary source for deliving content fails to make use of the primary benefits of the FileMaker client for rapid development and server security. If you're going to not use the FileMaker Pro clients, I would save my money and just use MySQL as the database engine. The benfeit of FileMaker is that you can make the User Interface much more rapidly than you can in PHP and your savings is in the development time. Personally, I think they will spend more money on the time in PHP than they will save in the FileMaker licensing costs. But if you've already done the PHP work, then FileMaker is not adding much value. Back on the security side of things, at least FileMaker is not susceptable to SQL injection attacks like MySQL is. There are a lot of good things about MySQL, but it is by far the most hacked database out there.