You are correct, EMS or Electrical Monitoring System protects against several potential issues, surges, spikes, over/under voltage, mis-wiring of cg pedestals. A surge/spike protector only protects one of these potential problems, thus they are less expensive- $80 vs $230. You get what you pay for , so to speak. You can get portable EMS systems that you plug into the pedestal and then plug your trailer into it as well as portable surge/spike units. The factory EMS is permanently installed inside by the converter.
The detachable cord is a personal preference, either one is perfectly fine, and both function the same whereas EMS and surge protection are somewhat different.
never in doubt, often wrong