All those apps that simply shows price fetched from coinmarketcap are nice for just one purpose - it's great project to put in your coding portfolio and to learn to code. Unless you are fetching prices from numerous exchanges, aggregate them, quantize, filter and deliver in user-friendly manner your app's customer value would not be exceeding coinmarketcap by definition. In short - I don't think another trivial portfolio watching app is something this market really needs, especially if it only works and totally depends on 3d party website that can change their API tomorrow and you screwed.