Considering I was told to do this by a Customer Service Rep at the beginning of the year when I couldn't progress through a Windurst Mission CS and seeing that other players have reported doing the same in these Forums, I think as long as you trust the person guesting, you should be fine.

I also did everything else the rep advised me to do, file checks, re-install, porting all to no avail before he arrived at the solution of guesting.