Probably better than no helmet, though my concern would be that this provides no real protection from abrasion for the face.

Motorcycle protective gear needs to protect from impacts yes, but abrasion is also a significant risk - slides from speeds over 100kph can be quite substantial in both time and distance - upwards of 5 seconds, and dozens of metres, pushing higher in different conditions.

This video of a slide in the wet made the rounds a few years ago: https://www.youtube.com/watch?v=DoYLKSYnrN0