The harnes system is werry comfortable, but might be a bit more weak that Ortowox if caugth in an awalache while using the beacon in search-modus. If you like simple searches, the Tracker. I'd want my rescuers to have it or one of the above. First of all, the M2 has an 80 meter range versus 30 meter range of the Tracker and a 37 meter range with Barryvox. Multiple burials with the Barryvox and the Tracker are extremely difficult especially if the buried beacons are within 5 meters of each other and deep vertical burials.
Safety switches are easier to use than buttons, especially in a panic situation.
With the analog external speaker, you always know how many beacons are buried. The Barryvox icon for multiple burials is a good idea, but, does not work. For example, if there were two people buried and you got to turn one of the beacons off, the multiple burial icon stays on until you turn the beacon off and recycle it. All automatic switchbacks to transmit are confusing and potentially dangerous with multiple burials and large deposition fields. I own an M2 and have never had a problem with it.