I've never used it, but I've heard some people have a problem with Control X. Another method is to create an object that exists to store flags, with flag 0 corresponding to moving left and flag 5 corresponding to hitting the fire button, for example. Then have all your events that would normally check keyboard states check whether those flags are set instead.
Then you have a group at the top of your events list, with the very first event being Always---[set all the used flags off]. Below that you can have all the events that set those flags, and have a mechanism for customisation as well.
That would be a -lot- more effort then just using the extension of course, but it does have some benefits.