It works just like the traditional ATM[mostly withdrawal although I’ve used cash deposit ATM direct before ], but it offers both deposit in cash to BTC into your wallet address and withdrawal from BTC to cash from your wallet address. Some could accept altcoins too depending on on how they are programmed.
Well while I haven't actually seen one before or made use of it ,true the Bitcoin ATM must be really reliable and accurate and Perhaps there are just two here in Nigeria. Basically the most confirmed location is in Lagos at Dazey Lounge and Bar, and it's around those Lekki and Ajah areas.
Make sure it a sane environment.. Infact, I will avoid using it in Nigeria but you’re free to do whatever you want you like . Just make sure you use your sense so you won’t have to regret it when you could have just done a normal swap or purchase of an online service.