[aragot]

How is it legal to talk about it?

Surely they've brickwalled them in the employment contracts saying "The employee agrees not to publicize events happening inside the company, with no limit of time, or the employee agrees to compensate the company for the loss of image"? How come the OP doesn't mind talking negatively in public about his former company?

I've already signed a simple software EULA which specified: "You (the Customer) will not comment about the performance of the product in public".

[nitrogen]

Contracts are not laws, and one would have to be very crazy or very well compensated for a non-disparagement agreement to make sense. I'll take my rights to free speech and coordination with my peers any day.

[pluma]

BTW, in some jurisdictions, a lot of clauses commonly found in contracts are invalid. Most EULAs don't hold any water in the EU, for example, especially when they contain "surprising" clauses (i.e. something a consumer would not reasonably expect to find in an EULA).