Out of all the direct comparisons (Mini 2, 66i, 700i), this is the only (first Garmin?) device with a flat antenna.
A bit of datasheet scrubbing shows different max power levels for Iridium between devices:
- Mini 2: 31.8 dBm
- 66i: 31.7 dBm
- Montana 700: 31.7dBm
- Messenger: 35.9 dBm
Clearly, all other devices share the same amplifier/antenna architecture while the Messenger is... different and 4dBm is a significant difference.
I am not an expert, but looking at https://iridiumwhere.com/ and knowing the low altitude of Iridium satellites (780km / 485mi), the visible satellites (usually 2, often just 1 or up to 3) will most often be low on the horizon, leading to differences based on the type of antenna and device positioning.
While I haven't found a way to get Iridium signal levels on my 66i, some rough testing shows that the vertical position works much better than the horizontal position, which is expected for this type of antenna.
The Messenger is clearly intended to lay flat and I would expect the highest gain of the flat antenna to be straight up, where satellites are not going to be most of the time.
This leads to the basic question: when used in its best possible position (horizontal for the Messenger, vertical for the others), is the messenger actually going to yield better connectivity? With Iridium delays being noticeable, any improvement would be great.
Note: For the curious ones, in a somewhat difficult location (partially obstructed sky plus vegetation), my small sample with the 66i led to ~5min average sending time in the horizontal position and ~2min average in the vertical position. With a clear sky, the average is < 1min.