Gps for canon cameras

I am modifying a GPS, for Canon cameras, to use the GPS REACH instead of bringing this device. The question is that if I’m doing RTK, how accurate are the coordinates of the photo GeoTac compared with using the hotshoe shot.

How do you connect Reach to the canon camera ?

I use one GPS for canon camera,
Modify it to use the reach , through the serial port the this.
If you are doing RTK , the photos are geotagged With this position