I had a friend use a similar thing on his water line. It worked ok when he was gone, but it detected a flow problem when he was watering the yard.
It would shut off the water when it thought there was something wrong, but there wasn't.
As a safety type thing, it worked ok,(I guess, never had to use it) as when he would leave for a weekend or on a trip.
Other thank that, it has to be tested one a month, and that turned out to be a waste of too much water.
Now If he leaves, they just shut the water off manually, just to be safe.