Personally, I would never take anything to Tanzania which would be a catastrophe if it were lost. Anything can happen. Its a very poor country and you will be seen as wealthy. They have a saying there, if you take a little bite out of an elephant, it won't miss it. You are the elephant.
No one can guarantee security. If they do they don't know what they are talking about, IMO. There are always petty thieves about. The good thing is that they typically won't harm you, they only want your possessions.
I have had things stolen (in groups I have taken there) in every kind of situation, including a Roman Catholic hostel where a man had all of his money stolen while he was in the shower.