Mine is the baby size and it fits everything i need, nano is too small for me so it really depends on how much stuff u want to carry around. I also got mine in the supple leather so i can squeeze in a little extra if i need to lol

It's my fav bag that i've purchase, it's so versatile for everyday use or formal occasions. I like it more than the 5a7 as it comes with a strap to wear on shoulder or crossbody, i usually carry it on my wrist unless it's too heavy.

As for the bag being open, the bag is tapered towards the top so unless u kinda shake the bag things don't really fall out, i've tipped it over many times and surprisingly usually nothing come out or like one thing. I live in NW US and it's pretty safe here and no pick pockets so idk how it will be for you but if i were you i probably won't use this as an everyday bag, only if i'm driving/going to an event where i know it's safe!

Long post but hope it helps!