I've been using PlotJuggler for a good couple of years now and it's one of the go to tools for debugging robotics systems for me. I'm sure it had saved me a good couple of days of my life!
I clicked on this link just out of curiosity but was delighted to see that it has support for PX4 ulog right out of the box! Pretty good chance this is going to become part of my daily workflow while working with autonomous drones!
It’s quite simple with ROS - you open a bagfile or connect to ROS, select the topics of interest and then you can plot the values.
An example of the top of my head for debugging: the robot I was working with was not very eager to turn on the spot, by plotting commanded angular velocity vs angular speed from wheel odometry I was able to see that commanded velocity was fine and the issue was on the motor controller level.