There is always a risk of a new addition bringing some nastiness to an established collection although if your friend has been taking good care of the skink those risks shouldn't be very high. I don't have very much skink experience but I do know that they are very easy to care for. A BTS is usually pretty tame so temperament and handling shouldn't be much of a problem. I know they have a more varied diet than snakes so they'll require more frequent feeding which means more frequent cleaning. Good luck!