They almost entirely are military market. A chipscale atomic clock is really only good for GPS-denied environments whether that means a UAV looking for a jammer

They almost entirely are military market. A chipscale atomic clock is really only good for GPS-denied environments whether that means a UAV looking for a jammer or some very small device underwater that doesn't have room for a traditional rack mount time and reference frequency source. Space (civil and military) is another application where you may have a satellite that is not in optimal range of GPS satellites and may need a backup reference. There could be some mining and petro industry applications but again, something deep underwater or underground. Anything other situation and you'd have clear sky for GPS.