At 8:20min in the video Ben spots a bug when Slider set to 100% does not save.
This bug is really easy to fix - in PlayerPrefsManager method SetMasterVolume we check if volume is in range between 0 and 1 - otherwise we log an error.
if statement there should include 1 and 0 as correct values but instead it exclude them (>= and <= instead just > and <).
Correct if statement looks like this:
if (volume >= 0f && volume <= 1f) {
PlayerPrefs.SetFloat (MASTER_VOLUME_KEY, volume);
}
Now we can save also max volume (100%) and min volume (0%)
Thanks to Bartek for the suggestion.