Well, Teensy is LOT more customizable!
But that also means you have to customize it, rather than simple use a ready-to-connect board. That means becoming familiar with the Arduino software. Teensyduino puts some examples in the File > Examples > Teensy > USB_Joystick menu, to help you get started. I'd suggest
installing Arduino & Teensyduino, if you haven't already, and then start looking at those examples. The basic idea is you have to fill in code that reads the sensors and sends the joystick stuff. It doesn't happen automatically, like a canned Leo Bondar joystick module, but that also means you have tremendous control over how it's done.
Of course, here's the documentation on the USB Joystick functions.
http://www.pjrc.com/teensy/td_joystick.html
You might also look at this thread about some work that was done to create an alternate joystick with as many controls as possible. Please keep in mind this is only the USB joystick side. You still need to add code to read actual buttons & sensors, just like the regular USB jostick stuff, but only a LOT more!
http://forum.pjrc.com/threads/23681-Many-axis-joystick
As to cost, Teensy is somewhat less expensive, but it doesn't come with those nice terminals to connect wires without soldering. If you're good with just soldering wires, Teensy could be a real bargain. If not, it might work out to cost more the Leo's module by the time you build up a way to connect and disconnect wires.