Be aware that there are members of the NTP pool with less-than-honorable intentions and you don't get to pick-and-choose. Yes, they all should provide the time, but they also get your IP address.
For example: unlike the IPv4 space, the IPv6 space is too big too scan, so a number of "researchers" (if you want to call them that) put v6-capable NTP servers in the NTP pool to gather information about active v6 blocks to scan/target.
Is this one of those extraordinary claims that requires evidence? Or is it generally true that there are homey-pots in many of these services (NTP, mirrors, etc)
Do you have any acticles or references about this? That would be great research (pun intended) to find out