The RAWs are not synched at all.
You're missing the point and the workflow. Raws DO have to be saved from card to some drive (desktop, laptop etc). That's step 1. I'd do that anyway and move on with the right tool.
With LrM now we must use Smart Previews.
We must now sync SP's to iPad.
We must then sync back. All the while, using a toy of a tool that is quite limited!
Instead I save raws to HD. Maybe I build SP's, maybe I don't (I personally don't).
I work on those images on a faster, color managed tool with all the functionality I need.
There's nothing to sync anywhere. Of course I do back up! That's another part of the workflow.
The solution is at best half baked. And the tool you have to use is half baked. Go ahead, use it, it's probably great for JPEG's much like Apple/iPHone/iTunes (add Drop Box and any number of other bits and pieces). For those working in raw? With more than a dozen raw originals? Seems like a huge waste of time to me. And at what cost of engineering resources at Adobe?
IF LR 6 comes out and blows us away, the last point will be moot. I'd hope they can build this iPad 'tool
a killer upgrade to LR but if not, I'm going to be worried the energies were misspent on LrM. Time will tell. For now, with a very good internet connection (56Mbps down, 11.63 up.), there's nothing I see that I find time effective let alone tool effective. But by all means run it if you find it useful.