A security review of three NTP implementations

So TL;DR Chrony has no broadcast/multicast, Autokey, or symmetric ephemeral modes (and at least two of those you don't want anyway). There's different NTP clock driver architecture (clock drivers talk to the server through a socket instead of being built into the server). The query interface is different, both on the network (separate port for queries) and admin tools (but not difficult to adapt--I flipped a couple of servers since reading the parent article).

OTOH Chrony boasts better statistical filters (which compensate for the lack of a clustering algorithm?), better power-saving behavior, better DNS pool behavior, and better tolerance for assorted network problems compared to ntpd and openntpd.