First I couldn't find it in the Google Play store. When I searched for it on the desktop, I found the app is "not compatible with any of your devices". Ho-hum.
I tried searching for local parking on the developer's site. They have data for maybe 10% of car parks in central Birmingham, UK; and even then the prices are denoted in US dollars. I don't know whether $4 = £4, or if some exchange rate is being applied.
If I search on Parkopedia, despite the slightly clunky interface not only is every local car park that I know of listed with prices, there are also details of the city street parking zones and their times of operation.
I would suggest that there may be more than one reason a particular parking app is more popular than another.