I have never used one in anger, but I have many: Raymarine MOB system, McMurdo PLB, inReach, and OceanSignals MOB1.
Practically speaking from the written experiences of many MOB situations, the three issues are: Realizing that there is an MOB, finding them again, and getting them back on board.
The Raymarine and Crew Watcher are similar in that you will get an alarm within seconds of an MOB event. It will take awhile, perhaps several minutes to take action and turn the boat around. The MOB may now be 1/4 away. In a seaway, you have a very good chance of not seeing them. The Raymarine sets a waypoint at the event, giving you something to navigate back to but discounting drift. The Crew Watcher provides a vector, but only over very short distances.
The PLB or inReach can alert authorities in SAR, but this is a very time consuming process. The Coast Guard will call the emergency numbers to verify that it is not one of the 99% that are false alarms, locate SAR resources to mobilize them, etc. It could be several hours before any are on scene, and if they have no way to contact the boat, the boat is searching blind. Also the boat might be many miles away by then, if the off watch is taking a nap.
This leaves AIS beacons like the MOB1. Within minutes, it will make a DSC call to your boat. If that is not acknowledged quickly, it will make an all ships emergency DSC call. Your current position will automatically appear on the chartplotter. This gives the best chance of finding the MOB by your boat, or another boat.
Of those systems I like the MOB1, and it's the one I take with me on deck for the night watch (offshore on the sailboat). It can be installed on your inflatable vest so that it starts up automatically when the vest goes off. It can be tested, and the tests use a small amount of battery capacity. The battery is expensive to replace. I don't mind having to replace it after modest use (what is modest use? 1 or a few MOB events? well worth it....). There is really no reason to test it frequently enough to be concerned about the battery.