Pardon the tech speak, but to put you at ease, we are going to go there…
hum uses multi-directional orbital pattern, normally called sonic vibrations, with up to 30,000 strokes per minute for the Rechargeable version and 20,000 strokes per minute for the Battery option, specifically intended to provide a safe brushing experience.
There have been numerous studies over many years proving the safety and effectiveness of powered toothbrushes in this "sonic" range of vibration.
So yes, hum is safe and dare we say, enjoyable because it avoids that aggressive brushing at the gum line where your enamel is thinnest. It’s one of those experiences you don’t know what you are missing until you try it.