Well, started out with a free 14 day trial from NTR.
Looks nice, seems simple to use, will see how it works out.
BOMGAR is probably next.
There really do seem to be a lot of these apps out there!
One I found, (which is really more suited to home users) was Crossloop based on VNC protocols, both ends need a free Crossloop account, and link in at the same time, but it was really very fast.
Also found UltraVNC’s Singleclick addin, which needs a little preparation, but looks like a nice single shot solution.
Effectively, you get the end user to download a custom single use secure VNC server, which only connects back to your VNC viewer, and deletes itself after the session, will be trying that out tomorrow.
These solutions are Windows only for now, though, and ideally, we would like to be able to support Linux and Mac as well, with one app.