Don’t forget to enable magstripe ATMs in your settings before using an ATM. I’m currently in Bali and tried a good 20 minutes to withdraw cash before I checked my app and noticed why all transactions were rejected. Wish I’d have read this first 
I only used my card once to pay at a restaurant but have seen MasterCard signs and card machines in a lot of places.
Edit: After two weeks in Bali I used my card several times at ATMs, restaurants, hotels and shops. Lots of places accept cards and only I had one hotel charge me 3% extra for card payment. Worked every time except once when my card didn’t seem to work on one card machine but worked on another one. I also tried using my card with the Bluebird Taxi app but the app wouldn’t accept the card. Although, I don’t think that was to do with Monzo as my other card wasn’t accepted either.