I love MiaTui bags - I've got several, including one backpack (think it's the Mickey one) which isn't the 'fake' leather but made of a water-resistant material which is really light. I feel it's very safe because it has a zipped pocket at the bag where I keep my purse, plus you can buy a bag clip which secures the outer zip, so it would be very hard for anyone to open it without you noticing.
I have a travel bag in the same material too, which folds away to nothing but is actually really roomy. I've used it for holidays as you can take it as carry-on luggage.