I used it before, it is not good at all, it is true that the fee is 0, but selling is at the lowest price and buying is at the highest price, so you will be a loser in the end.
Everyone prefers to place orders to sell at high prices that bring them good profits or to buy at low prices. You will wait for some time and pay some fees, but you will get what you want.
The only benefit I have found for this tool is that when you are in a hurry and want to buy or sell regardless of the price then you can execute the transfer immediately.
Now it makes sense on why the fees are zero but other than it, I think this tool is built for the casual customer of the exchange or those who are not really a serious trader who trades from time to time. Like me for example. Last time, I only used Binance to trade small amount of crypto to the other and I found out that I can't sell them in the spot trading because the minimum amount is too high.
I try using other pairs and the minimum there are also high. Fortunately I found that convert feature and that is how I trade my coin. I notice that this feature is also present in Trust wallet but I guess that is because Trust wallet is still associated with Binance.