I think a while ago my dentist suggested that a quick brush with a manual toothbrush would likely clear more out than an equivalently quick brushing with an electric toothbrush (rough theory: you can move it faster and cover more surface area). But he claimed that electric is better if you use it more thoroughly. I also disagree that an electric toothbrush converts to a manual one. I think it converts to an unusable bad manual brush because the electric toothbrush is too heavy to move quickly.

Another toothbrush tip: toothpaste is mildly abrasive and can be used as an emergency polish if e.g. you’re in a hotel getting dressed for a wedding and realise your silver cufflinks / novelty Texas-shaped belt buckle / whatever have become tarnished since you last looked at them. An electric toothbrush can help a lot here.