If anyone reads the IET's Engineering & Technology magazine, in the
current issue is an article "Electrical industry fights fakes".

It has a picture of counterfeit and genuine MCB's side by side with
the covers removed.

The fake has literally just a crude switch inside it. No current
sensing or fusing. Unless you opened it up or tested it with an
overcurrent, you would never know (until it failed to trip when
necessary and your wiring melted).