Flaws in your squat technique will hold you back from progressing. Overhead squats can improve the squatting pattern and should be a regular part of your strength training program.
The overhead squat requires a more upright posture than the back squat and you're forced to execute the squatting pattern precisely, otherwise the bar would drop to the front or back.
Have a look at the video. You can see the high concentration level of the athlete and accurate execution.
Dan John wants to know if you're making progress. It seems the answer should be simple, but is it? Fortunately, the big guy offers up 3 unorthodox ways to gauge your answer. (Wait until you read about the "pencil test".)