Just attaching the M2 isn’t going to get you the ability to get RTK values for the geotags. That involves writing to the images as they are shot as it would with a Phantom 4 RTK. Almost all retrofits are used with PPK and there is processing of the GPS logs and retagging of the images involved. How large are your sites? If there are areas that can be designated for GCP’s that you can keep somewhat undisturbed then I would forego the M2 and just use the RS2’s that you already have to set targets.
This is probably the cleanest kit for adding PPK.
https://topodrone.org/product/kits/pro-uk/p4-uk-ppk/
We have used this one with the addition of an AShot which replaces the light sensor and the need for an external battery as they have shown. This captures the exact timing of the images for creating the events in the GPS logs.
http://www.tuffwing.com/products/Phantom_Reach_PPK_Integration_kit.html