I wouldn't mess with your fuel lines, they run at high pressure on a fuel injected car and if you get a leak the car could set on fire - and you may be in it at the time!!!
These 'fuel saving' products have come and gone over the years and as far as I know non of them do anything - the only 'magic' about them is the way that they magically transfer money from your bank account to someone elses. If you want to save even more fuel in a jazz, the only way to do it is to drive more carefully.
Just remember the good advice that 'if something seems to good to be true, It undoubtedly is'
