it does what it says!
I can literally watch the bars on my phone jump up. I've been told that I shouldn't use this metric as it's not always accurate so I went ahead and did a speedtest also. I'm seeing 4x the signal strength on average.
I've also tested it in areas where I do not get signal. I might get a LITTLE further into the area, but if you are in an area you see "signal lost" and the call dropped, you are likely to see similar results with this booster. It can't make signal where there isn't signal, only improve poor signal.
I am incredibly satisfied. My calls are clear. My only wish is that there was a replacement solution for my OEM antenna. My car doesn't have a roof (soft top convertible), my trunk is made of carbon fiber, and I do worry about the magnet mount. If it bolted through the hole for the radio antenna it would be much cleaner.