The age old advice: don't invent new cmds to bind buttons to. People are stupid and don't know how to bind their shoelaces. ;-)
You can look at a plugin I made awhile back: The Stealth Bag:
http://forums.alliedmods.net/showthread.php?p=85752
It has progress bars, and uses the normal USE button for everything. No new cmds to bind buttons to needed at all.