This may have been overlooked in all of the new Arca announcements. This appears to be a newer LIGHTER, version of the old tried and true M2. I noticed the weight for the unit is around 2.64lbs, I assume no rail included. They are making it in 3 versions, DSLR, Medium Format back, and 4 x 5. The rear mount appears lower or higher depending on the camera being used. This unit does have a 32mm limit on widest lens.
In the photo Arca has the standard rail included, which I believe would need to be added to the total cost.
This unit seems to have all the great movements of the larger and heavier M2. Since it has the R mount any R lens can be used. If Arca comes out with Nikon, Canon, and other mounts supported in the R mount this could be an interesting alternative.