NDA and non-disparagement are radically different things; I have zero issues with NDA, I'd take umbrage at not being able to say a place I used to work at sucks.
See here: http://www.washingtonexaminer.com/silenced-workers-who-lost-...
Regardless it's pretty juvenile and self-destructive behavior to go around disparaging an employer for firing you to begin with. Getting a cash bonus for the self-censorship a rational adult should be exhibiting anyhow, is not such a bad thing
It keeps you from posting honest glassdoor reviews (no cons/negatives and zero faith glassdoor wouldn't release your info on discovery), telling friends what it was like to work there, etc.
Onto your specific point, N-D is not unusual for senior employees with strong contacts in the company's target market (like e.g. sales & project management). They're not necessarily a sign that the company is doing anything shady, but they are a strong tool for preventing disgruntled former employees from saying bad things which might hurt a business. They're pretty aggressive, granted, but they serve a purpose. Most people's umbrage can be satisfied for a price.
Not unusual for junior employees either.
>they are a strong tool for preventing disgruntled former employees from saying bad things which might hurt a business.
It prevents you from saying entirely true things which might hurt a business that fully deserved it.
So, I wouldnt have a problem with a company not wanted to litigate false claims, but true claims being muzzled is another thing.
For instance if I say, "I liked working at Company X but I think the CTO lacked leadership skills/vision" that's disparagement. It subjective/opinion, but assume you have factual reasons you could use to back-up how you formed that opinion.
For example, PA law:
* The statement is false;
* The publisher either intends the publication to cause financial loss or reasonably should recognize the publication would result in financial loss;
* Financial loss does in fact result; and
* The publisher either knows that the statement is false or acts in reckless disregard of its truth or falsity.
There is debate regarding the efficacy of non-disparagement clauses for a variety of reasons, but it's often tough to make them stick.