Anyone tried one of these "Kiwi" fuel saving devices?

Not really, once you read what the bad habits are it’s pretty easy to change your driving style without a gadget to remind you. Just make some simple changes now, and track your mileage. This isn’t rocket science; it’s just slowing down, being less aggressive, and learning when to shift.

I guess it varies by person and just how frugal you are with your money but increasing your gas milage by 3 mpg just isn’t that big of a deal to me to make me want to seek ways to get it.
With gas at $3.50 and driving 15,000 miles you’re going to save a massive $194 a year. $16 a month. $3.75 a week.
If someone told me they’d pay me cash to change my drivng habits for the week and then coughed up $3.75 at the end of the week I’d probably just tell them to forget it.

I don’t drive a manual transmission car anymore.