Ask HN: In the mobile app world, is field testing > unit testing?

I have a general software dev question, since I'm new to mobile development.

Overall, it seems that with any mobile app, you have to dedicate a significant portion of time to conducting extensive field testing of your app on a variety of devices.

On top of that, if you follow TDD, you need to write unit tests for as much of your app as possible.

But as an indie developer, lots of field testing is really costly, but so is writing test cases for everything.

So my question to fellow hackers is:

Is it appropriate to trade off unit testing, in favour of more field testing? OR is it better to have a balance?

Thoughts?