The "mode lock" is a modification which Canon will perform on the 7D and 5D Mark II where they add a button to the top of the mode dial. It locks the mode dial and you can only turn it when the button is pushed (to prevent you accidentally turning it).
It costs $100 in the US (not sure about other places) but I guess the reason it's listed as a con in the review you found is because they don't offer it for the 60D or 550D.