Of course, anyone who actually is prohibited from possessing (and therefore carrying) a firearm cannot be compelled to disclose that they are carrying a firearm.
I'd be interested to see the constitutionality of the bit allowing detention challenged, but I'm afraid we'd wind up with a ruling that the government's interest in ensuring that they aren't turning loose prohibited persons with firearms outweighs any private interest in not being detained while police "make sure you're legal."
As I read it, they would still need a reason (excuse) to make a stop, at which point the person stopped (if carrying legally) would be required to disclose and the officer would be authorized to prolong the stop in order to verify. That's not to say that some departments wouldn't need to be bench-slapped. Currently, anyone carrying with a license has a duty to disclose when stopped and an obligation to provide their license upon request. At that point, you're kind of stuck until the officer gives your license back. This doesn't seem like it was meant to be a huge change from status quo, as far as police interaction goes. It's bad, but that's because it's based on what we already have. This fixes one problem, but it doesn't fix all of them.