Digital testing is very expensive. It can be a bit time consuming to run all the tests but the important ones are pH, Ammonia, NH3
If you test for those 4 you're good. I'll be honest, I don't test as much as I should...but you can see if your fish don't look healthy. Even a slight amount of ammonia leaves tell tale signs so its the first thing I test for. Once you have an established tank and are doing partial water changes...that's my main test.
The others I every so often just to make sure they're ok, which they usually are.