I have tried three of these boosters, and this one is the best so far.  One piece goes in a window facing the closest cell tower.  If you have low E windows or metal screens, it may interfere.  Then you run a cable from that piece to the second piece, which can be up to 25' away.  In our case, it adds about two bars to our signal strength, which is a nice boost.  Easy to install and does what it it supposed to do.