I've also used RealVNC successfully.
At one time I actually had a PC in my network and I controlled it entirely via RealVNC.
Likewise, the only problem I found was it being slow in responding to any changes in the remote PC.
For remotely connecting and repairing another PC I would think it would be ideal, but not forgetting the other person would need to be around to re-connect should you need to re-boot the PC (If I remember correctly)
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Actually I'm glad you raised this question as I was thinking of using it again but could not remember the name of it.
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If it ain't broke.
Don't fix it.