I think the type your refering too are the ones with the tabs you have access to with pliars, the type the tool above are for are the type with no external tabs , the tool basically wraps around the outside of the line and the raised ridge slots into the connection of the line and relases the locking tabs so it can be separated.
As for the line separating problem you had ,yeh thet can sometimes be tricky. I find with most if you push the tabs in and kinda push it first (opposite from the way you think you would to remove it) and then yank it back they come free. I guess alot of it is experiance. I bet if you saw a tech do it you would kick yourself
