welcome to the community! 
for iPads, its better to use coda in safari or on a web browser app.
there are a few quirks to it as compared to using coda on a web browser on a computer but in general it has almost full functionality (and similar performance).
Namely, scrolling to find a page in menu side bar reorganized them instead (but maybe thats user fault lol) and it is more cumbersome to build (edit formulas etc).
But definitely can vouch for ipad / safari setup as a few months ago my laptop croaked itself whilst on holidays and on my ipad pro i was able to build mckinsey style charts & dashboards for one client and a complicated Projects and Tasks (Work Breakdown Structure) with lots of conditionals etc for another client. Those were fun times 
as for the mobile app.. i would say it is not very reliable / usable at the moment but am under the impression that its going through a revamp??
there’s an upcoming roundtable for this topic (see below) and maybe we will get more definitive answers then.
hope this helps!
cheers!
Mel