Yes it is safe. This UAC control will always pop-up because there's a syncing process that will happen if you agree with it. However, it is not a threat.
I haven't yet seen any explanation of what this does - telling anyone that there is a syncing process totally avoids the question and does not define what it does and what we are getting involved in - is it a genuine MS initiated process? - why is it dangerous not to get involved if so why? It would be helpful if a clear response from someone with the knowledge would clear up this issue once and for all.