It has lots of poor reviews.
For Android you can use openandromaps which are free but less detailed. 20m contour levels etc. Orux maps works fine on Android (free) and the maps get updated regularly. Maps exist for most of the world. Did I say free? Runs on my phone OK.
I happen to use Anquet on the PC and print out paper maps for my use. But Anquet is not cheap, £400-ish for all of UK at 1:25k, 1:50k, plus road atlas and height database. Anquet is OK on Android, you enter tracks etc. on the PC and sync that to the Android device. A colleague has a 64GB SDcard in a Moto-E with full Anquet 1:25k & 1:50k with him.
OS mapfinder is free and you can get some mapping data for not much money. You can try it and see if it’s any good.
Questions to consider: the data I buy, how many devices can I put it on? Do I have pay each year? What happens when I buy a new phone? What happens to my investment if the app is discontinued?