It is possible to use such things somewhat safely, though I must confess I don't think I sandboxed any installs of this unless you count having them inside VMs for some things. Also after you have tried talking your elderly relatives through whatever operation they are trying to do this week over the phone (probably trivial for you, hard as you like trying to translate it and worse if things are not in alphabetical order because someone clicked and dragged or something) then you will begin to appreciate the sentiment behind the great album title "give me convenience or give me death".
Reading around though it seems it might be people that have accounts rather than just numbers, not sure about simple unattended access. If it is just accounts then that makes my life easier -- I usually do not do any accounts so people have to phone me and tell me numbers as it gives them a false peace of mind (more than once I heard it is scary seeing the mouse move and files being opened or similar, yet my command line or SSH fun does not even register).
Teamviewer PR also seem to be handling it very badly so there is at least the breakdown of what they have done there to look forward to.