I'm from Debenu. The main difference between PDF Tools and PDF Maximus is that PDF Tools is available from the context-menu in Windows Explorer and lets you work on one PDF at a time where as PDF Maximus has a batch processing engine, along with watched folders, and can process lots of PDF files at once. It also lets you create workflows by adding lots of different actions such as split, stamp, secure, etc, to action lists.
There's a lot of overlapping functionality (such as split) but the two tools are used in different ways.
If you've got any other questions, let me know.