I have never used a Bitcoin ATM, because I don't see the point in it. You can buy and sell crypto on the exchange or even in a wallet.
It's similar to the difference between a convenience store and a supermarket.
Sure, most supermarkets will probably be cheaper, larger, etc, but sometimes they close earlier, or might be far away.
That's when a convenience store would make sense. In specific cases where you need to go there sporadically.
With a Bitcoin ATM, imagine traveling the world and going anywhere, and you only need your Bitcoin wallet to get local cash, without using any banks. Quite convenient.