This app does not magically increase your signal strength. It shows the same information you have, only 100 times larger.
This app was developed for use in rally race cars. Between racing stages on the transits, the race teams often want to contact their crew to give them info on repairs needed. Travelling down a bouncy dirt road watching for when you have enough bars to get a text out is difficult.
Note that in order to get your signal strength, the software has to ask the phone for the data from the cell phone chip. This comes all as one bundle which includes the cell tower information, which means that one could in theory (although this app doesn't) figure out roughly where the user is if you had some other master list of all cell tower locations. Because of this, the app needs the "Coarse_Location" permission to function.