I’ve recently been to various places in Angola on a business trip, I never needed to use my Monzo as I had my company’s supplied money and cards. However I’ll write here what I experienced, as I have not seen an Angola category and for future reference, should a Monzonaut ever need to go.
Almost all cash machines and POS in shops, restaurants, bars, hotels… are all for local cards only, VISA and MasterCard can only be used in a handful of places country-wide, I only ever spotted one ATM which accepted Mastercard and it was situated in Luanda airport. One of the hotels I stayed in was VISA only, you couldn’t use foreign cards in any of the others. Make sure you bring plenty of money with you.
There seems to be two exchange rates, the official one and a better one. Official is what you should get in banks/exchange places (some hotels will fleece you with terrible rates) but if you have local contacts, they may be able to get money exchanged in street for you for way better rate than official, you could be getting twice the Kwanza than exchanging at bank. Extreme caution and all that, make sure a local haggles for you, Angola and Luanda specially can be quite dangerous.