We strongly recommend that you wear a protective helmet whenever you ride your bike. Keep in mind that the protective capability of helmets is proportional to the speed of the bike (whether you are on a regular bicycle, an ebike or a moped or motorcycle). Our helmets are geared to speeds at or below 20 mph. Faster than that might require something like a motorcycle helmet.
A bike helmet provides some protection in any crash, but not enough for a powered vehicle consistently traveling at 20 mph and higher. You are taking a greater risk than a bicyclist that the helmet will not be adequate for the type of crash you should expect.
For bike riding that consistently exceeds 28/mph it would probably make sense to consider a light motorcycle helmet.