This Humber Tricycle was really just a high-wheeled bicycle with the addition of a second front wheel. You mounted and rode it just like an Ordinary, the only major difference being that you powered the front wheels through a chain drive.
The Humber was notably fast and its extra front wheel added lateral stability. The riding position reduced the risk of headers, at least on level ground. But riding this Tricycle was not as safe as it might seem.
One particular danger was hitting a stone with a front wheel: because the wheels were connected, this could turn both wheels at the same time, causing a sudden swerve. If you were going fast enough, that swerve could tip you over.
Coasting downhill was particularly dangerous since, as your weight naturally shifted forwards, the small back wheel would lift off the ground, leaving you unable to steer. If you then hit a stone, you would almost certainly crash.