What is the best way to Debug PX4 code?

Dear all
I’ve read the docs and can see that it is apparently possible to debug PX4 using a Drone code probe. I’ve also noticed that there doesn’t appear to be a lot of people using it, judging by the low number of messages or instructions relating to it’s use.

However there are clearly a lot of people doing very detailed development work, so I’m puzzled. How are you guys doing it?
Are you doing the equivalent of “printf debugging” ?. i.e. putting print statements wherever needed in the code.
How is this done in practice? I’ve seen in the code that there are DEVICE_LOG messages, but although I’m connected directly to the console with a probe I don’t see any messages coming out apart from the booting related ones.
Do these Debug messages need to be enabled, how ?

Or is the preferred way to use PX4_INFO style messages as in: http://dev.px4.io/v1.9.0/en/apps/hello_sky.html

Any tips really welcome, I’ve got some issues with the PMW3901 Flow sensor that I would like to try to troubleshoot and don’t know how to go about it.