I mostly have used this app to compare coverage between carriers but if you have a decent network connection and you are only interested in one carrier, then it seems you get much more detailed and fresh info at the carriers own websites. Really no reason to use the app in this case. As of this writing, I am only seeing very, very broad coverage and trying to zoom in on something the size of an rv park or even a small town is almost useless. If you care enough about spotty coverage areas to need this app, then the fine details are probably important... Like which side of the lake might get coverage? This app isnt telling me that for my current location but carrier website does.
This app does work without a connection, which is marginally useful at best. Perhaps if you are way far out from coverage area or a free wifi hotspot to jump on for a few minutes? Or to save a little on mobile data? If the signal resolution were as good or even close to carrier websites then it might be handy to have it stored offline for instant access. But even then, if the data isnt fresh, then not so much.