Maybe enable animating the changing of the label value?

[acosmicflamingo]

Great work with this project! I'm integrating it to my app right now and am making a change to it that will suit my needs, and I think you'd like it too :)

Instead of just instantaneously changing the label value, how about you add something like this?

private func updateProgressLabelText() {
    UIView.transition(with: progressLabel, duration: 0.8, options: .transitionCrossDissolve, animations: { [weak self] in
        if let currentSelf = self {
            currentSelf.progressLabel.text = "\(Int(round(currentSelf._progress * 100)))%"
        }
    }, completion: nil)
}

I don't know, maybe you thought of it already. Wouldn't hurt to share my findings! Take care and once again, great work!