They are also smaller if you DO have a cloud membership so it is no different.
They're not cut in half; they have a maximum of 2048 pixels on one side.
The time you sync the images from Lightroom to Lightroom Mobile, only the Smart Preview of the images will be synced.
And the size of the Smart Preview is quite small, also Lightroom Mobile is only available with Creative Cloud Subscription.
Thanks so far, but I have another workflow: 1.) iPad Pro with camera connection kid, bring the photos directly in the iPad pro. Than I want to work with the photos and later bring them to Mac. What´s about the sizes of my pictures? 2.) iTunes Snyc some photos from iPhoto. Than work with them in Lr mobile and bring them in full size back zu Mac. How does this work?
If you sync the images either ways, the Smart Previews would be synced on the devices.