Summary: The now-discontinued M2 was a solid performing single-antenna beacon.
Searching: The long single antenna in the "M" series provides a long reception range. However, as with all single-antenna transceivers, you (and not the transceiver) must interpret the flux lines to locate the victim (versus multiple antenna beacons that display a direction indicator). Likewise, single-antenna transceivers cannot compensate for spikes (which you can compensate for with good probing). Although I was a big fan of the Ortovox single-antenna beacons for many years, I personally feel that the advantages of multiple-antenna transceivers no longer make single-antenna beacons the best choice for most users.
The M2 is primarily an analog beacon. The audio signal is always analog (the volume increases, but the tone and cadence remain constant). The digital portion of the transceiver kicks in when you are within approximately 30 meters (and the distance indicator displays 40 meters). At this point the M2 displays the distance to the transmitting beacon. Although the M2 does not have a direction indicator that points to the victim, an arrow on the M2's display darkens when it receives the strongest signal (i.e., when it is aligned with a flux line).
Controls: All analog Ortovox transceivers turn on via the harness: when you put it on, it turns on. Most of the other transceivers turn on via a switch. People familiar with the approach used on the analog Ortovox transceivers have reported that they sometimes forget to turn on the manually-switched transceivers. You know what they say about teaching those old dogs new tricks! Changing to search mode is fairly intuitive.
Comfort: All of the Ortovox harnesses are comfortable. The M1 and M2 are relatively large. The long banana-style allows for a long and effective, albeit single, antenna.
Other: The Ortovox M1 and M2 were recalled for a replacement battery door. The (free) door might still be available.
The gray M2 is very similar to the M1. It was first released in 1999 and the blue version was released in 2001. Manufacturing of the M2 was discontinued in 2009.