It's difficult to say how testimonials go, some people seem to have dubious reasons, others may actually believe that they're getting the real thing.

Some owners may love it for a while, then realize (as their driving style returns to normal from the 'auto-tipid' mode they unconsciously assume after buying the device) that it really doesn't make much difference.

The disadvantages to trying out products like this are varied. The EGO would not have much of an effect on your car, and taking it off would be relatively painless. An intake-based "fuel-saver" may do temporary or permanent damage to your MAF or throttle, depending on what it does. Fuel-line magnets would just make you feel like a total idiot when you take them off.

Go ahead and try if you like, but there are much better things to spend P6,000.00 on. I would buy every single fuel saver on the planet just to prove that they don't work, but I wouldn't spend my own money on them.