What do you mean? Will the Birger route be less easy?The mounts have not caused me any issues yet in terms of backfocus. So far, they have been on after each swap. With the Birger mount you are removing the backfocus collar so I can't comment yet on how that will affect things. But in terms of Nikon mount, just do a backfocus check when you swap back and forth and make sure everything is still in alignment.