The 010-10813-00 Mini-B Data cable converts the TTL level data from
the Nuvi to RS-232 data levels, but leaves the data in Garmin Binary
The Gtrans cable does that too, but also translates the Garmin Binary
data into Standard NMEA sentences, which are much more user friendly
for APRS applications and the Kenwood D7/D700/D710 radios.
If you want to use any of the listed Nuvis with an OT2m, then all you
really need is the 010-10813-00 Mini-B data cable. OT2m have the
Garmin to NMEA translation built-in.
If you want to use any of the listed Nuvis straight to an application
needing Standard NMEA sentences, or an above listed Kenwood, you will
need the Gtrans cable.
Hope that clears it up for you.