Encoders are fantastically useful devices for human-machine interfacing. The issue for the makers, teachers, students, and engineers trying to use them is that many have less-than-ideal output signals. Output lines will ring like struck bells whenever the line changes state. Some encoders ring so much, it’s like they’ve been designed to interfere with themselves. It’s kind of like trying to listen to a person giving you instructions over a walkie talkie. You can usually tell when they are saying something, but you aren’t always sure of what.
This is probably doubly true for encoders at the extreme low end of the cost spectrum. This doesn’t mean that low-cost devices are useless or not worth your time, but it does mean that you will have to exercise more care to get them to operate reliably.