Briefly, if you imagine a bit of metal on the edge of a spinning gyro, then to turn the gyro you have to stop the bit of metal moving in its current direction and start it moving in another direction. To do this when it is moving fast you have to push it rather hard. My prototype gets lighter when I turn it on Weighing something which is vibrating on ordinary scales is a sure way of getting a wrong answer. As a result the weight reductions reported for such machines are always close to the limits of accuracy of the scales used. Both of these questions come around fairly regularly.
Some companies sell magnets which clip around pipes.
Sometimes they are sold for use in hard water areas, where they are supposed to prevent the buildup of limescale. On other occasions they are sold for cars, where they are supposed to increase fuel efficiency. Neither of these claims has ever been substantiated by careful testing, and there is no theoretical explanation for the supposed effects. The advertisers try to make it sound like there is, but its actually just pseudo-scientific eyewash. Note that in some cases installing the fuel magnets according to the instructions will give increased fuel efficiency.