Well, I have 5 Charlie's so I love them! The washed red was my first one. I added chalk next then the Keith Haring embellished one, and then recently added Ivy and Marine through eBay purchases. It's very easy to carry, accessorize, etc. Did you know that you can customize the Charlie online and in select stores that have a craftsmanship bar? I am going to be embellishing my chalk one with stars & rivets soon.
I personally never use the crossbody strap, however I have seen others use the more substantial embellished crossbody straps and they look great. It's a matter of personal preference. I tend to carry mine in the crook of my arm. The center compartment is not attached at the bottom. That said, I have not experienced any items, small or otherwise, sliding from one side to the other.
My Galaxy S8+ fit in one of the slip pockets attached to the center compartment. My work badge fits in the other. It's a very well organized bag, which is why I like it. The leather is initially stiff when first purchased, but it softens up with each use.
Let me know if you have any other questions that I can answer.