I have downloaded app as I have read about their visa cards which have some unique features. The app is also used for trading alongside the web exchange. I usually use the app and trade ZOOM which are needed for cards (up to 100k for the highest tier). After using the app for a while I think that the design, menu and features of the app are little bit confusing. You can be sometimes lost.
The fees are reasonable but there are only few trading pairs. It is obvious it is not mainstream exchange. There are also better cards provides with better cashback and services but still it is worth to try ( at least there are some features more oriented for CoinZoom itself).
Overall you can try it but do not expect to be the main exchange for you.