What does FreeMemory actually do?
Absolutely nothing other than swindle people out of their money. Don't ask me why Apple approved it. iOS and OS X manage memory as required. A lot of FUD out there claiming it's poor at it. No evidence to support those claims. No facts ever presented. No one with a modicum of experience or education in the field has ever come up (that I've seen) and accredited the claims. Snake oil.

You want to improve performance? Buy a better device. Only better hardware can equate to better performance. You can of course optimize a system, but this doesn't do that, it only shifts available memory.

Here's a breakdown of how to understand memory management in OS X (courtesy of Apple):


  Free memory
  
  This is RAM that's not being used.  
  
  Wired memory
  
  Information in this memory can't be moved to the hard disk, so it must
  stay in RAM. The amount of Wired memory depends on the applications
  you are using.  
  
  Active memory
  
  This information is currently in memory, and has been recently used.  
  
  Inactive memory
  
  This information in memory is not actively being used, but was
  recently used.
  
  For example, if you've been using Mail and then quit it, the RAM that
  Mail was using is marked as Inactive memory. This Inactive memory is
  available for use by another application, just like Free memory. 
  However, if you open Mail before its Inactive memory is used by a
  different application, Mail will open quicker because its Inactive
  memory is converted to Active memory, instead of loading Mail from
  the slower hard disk.


Now even with rudimentary understanding of memory management in Apple's OS, tell me if you think "freeing up" Inactive memory is of any use? It is available to any application that requests it and if the same application wants to grab a hold of it again, it gets a speed boost. It's of course not this simple, but razing Inactive memory and moving it to Free memory results in no increase in performance. After all, how could it? A good system should hoard all your memory and allocate it to things that need it. Free memory is wasted memory as it's, by definition, not being used. If you have 8 GB of RAM and keep 4 GB free at all times, then you have a system running 4 GB.

Inactive memory in OS X is allocated intelligently. I'll change my tune when I see valid and reliable data that claims otherwise. And honestly, if nothing else, do you think some third party app has found the holy grail of memory management that has eluded Apple's world class engineers all this time (not to mention the thousands of contributing open-source UNIX programmers)? Like I said, snake oil.