Interesting that the 55 has more resolution options than the new 56, and the 56 has a larger micro SD card capacity (256gb) than the 55 (64gb). I use a 128gb in both 56's. I've never tried a 256gb to see if it would work.
1. Garmin Dash Cam series have larger screen than Garmin Speak Plus.
2. Garmin Dash Cam have Forward Collision Warning System (FCWS)
3. GPS-enabled Dash Cam models record your current position and speed while recording video