I wouldn’t really be a fan of having a picture on the card itself, since you can’t use the card as a form of identification and it could potentially put some people off the idea of using the card (for fear of drawing a few funny looks).
I think having a sort code and account number on the card would be a great addition - I’d imagine this will come with the full banking license.
At the moment though, I don’t really feel like the app is any less secure than, say, my NatWest account for example. In fact, I actually feel like my Mondo account is more secure on account of the fact that the only possible access to the account is done through my iPhone, protected by Touch ID and within 3 feet of me at all times. When you add to this the fact that you can instantly freeze the card from within the app and almost the very second a transaction is made, I get a buzz on the wrist and I see the notification on my Watch, I really feel like it’s pretty solid security wise.
I’d like to see a bit more ability from within the notifications, though. I think the ability to quickly flag a transaction as suspicious from a notification action would be really handy, given that as soon as you notice the transaction you could flag it and freeze the card, in theory stopping any further use beyond that first transaction.