I took this to my Mexico trip and felt safe leaving the majority of my money in it back in the room.  I took all my spending money with me after hearing some bad stories about ATM's or using your credit cards.  The only challenge was finding something secure enough to wrap the lock around to actually make it secure, but after a little hunting I found a good spot.

Takes up very little space in the suitcase and will easily deter a casual thief.  I'm sure a more dedicated thief could find a way into it or cut it loose with the right tools.