Why is an NDA reasonable? I am really curious of the mechanics of a startup that would make this different from any other company under that law.
Though of course, any such NDA should be revealed ahead of time, including the precise language of the NDA, so that investors (and yes, employees who receive equity in lieu of cash are investors) make a fully informed decision.
Is this a common thing with NDAs? ISTM it's rare that during the hiring process one would receive a folder containing all the NDAs one might potentially be asked to sign while working at a firm. One might receive an "initial" NDA, to sign before starting, but every time there is an ownership change one can expect a new round of NDAs, because apparently NDA terms are a rapidly-evolving area of contract law.
What's going on in this world where your phone call is recorded, yet people sheepishly suggest "oh maybe a NDA is okay here, ya know".
Don't want all your private company secrets legally broadcast to the public? Be careful who you grant shares of ownership to. Can't trust your employees? Guess you have to find something besides ownership to incentivize them with.
The law in DE states that he has a right to see the data anyway if he has a valid reason, and "valuing my shares for tax reasons" is a valid reason. So NDA or not, the company needs to show him the numbers.