I've got an M-Audio EX-P and while it's quite an inexpensive unit, it shares the same fatal flaw as many other expression pedals. Their weak point is the plastic collar on the pot shaft.
Mine was cracked and kept sliding off. Luckily it can be easily fixed! While the pedal was open I decided to replaced the hard-wired cable with a quality TRS jack since those plastic moulded plugs are notorious for failing at the most inopportune time.
Finally, I threw a mod in by adding another TS jack which I can dasiy chain another footswitch. This lets me get both expression pedal capability and external footswitch operation without having to keep swapping which unit is plugged into my MIDI foot controller.
I've got a detailed write up with lots of photos here (http://blackaddr.com/expression-pedal-repair-and-mod/).
http://blackaddr.com/expression-pedal-repair-and-mod/
Hope you find it interesting.