I joined Monzo after doing some research to find the best way of spending money abroad. My old bank would charge me extra fees for using my card, using ATMs and then even give me their own exchange rate which was far poorer than the actual one from Visa/Mastercard. Monzo is a far better alternative as they don't charge these fees and give you the actual exchange rate i.e. the one you find on Google.
The app feels very slick and user friendly, which makes it easy to keep an eye on and manage the money you have coming in and going out. I've actually now started using it as my main bank and way of spending in the UK too. The customer service has also been excellent, I received a quick and helpful response after contacting them first with a question.
It was also a nice bonus to get a free £5 put into my account for signing up first using a friend's referral link. If you're thinking of joining, feel free to use mine and you'll get it too.