i have had one in each car for years. since i smell like cigars, sheba smells like cigars, i don't know if it works but it looks official with the two green lights.
if you go away for a week or so, remove it from the car that's sitting, it draws enough in a week to discharge your battery. on regular days when your drive the car 2 or 3 days a week, you won't have a problem.