The "Bitcoin BCH" user recorded a movie in which he double-spends on Bitcoin using the Replace-by-fee function. Someone may find out - what kind of Bitcoin is bad that he added this option, but the solution is simple - Bitcoin Cash / BCash.
But doesn't the author of the movie want you to think so by manipulating / lying you?
It is not possible to create a double spend on BCH
The website https://doublespend.cash/ shows every day how many people managed to make a double spend. It can be considered that there are few of them in relation to the number of transactions and this is true.
If this "bug" can be fixed in BCH, will it be possible to accept 0-conf payments safely?
The answer is no. The concept of double spend does not mean attack, but a certain group of attacks. Attacks where the transaction is sent to many people. Such a thing can only be done if the seller does not make sure (does not wait for confirmation from the network, which can take a few minutes) that the transaction is 100% irreversible.
I will give you an example. I'm a miner and I have 35% of the processing power, which gives me a 1/3 chance (statistically) to mine a block.
I go to the store, I make a 0-conf transaction. In the meantime, however, I have created a new transaction which I have not propagate to others and as a miner I will confirm it.
It is not possible to detect this attack until the transaction is confirmed. No matter how many millions of dollars you have in your double spend detection systems.
Is there an option for secure and fast transactions?
The first possibility is to use a well functioning Lightning network. BCH users can use this network thanks to Liquid Network, although it is not so widespread there.
The second option is to use an intermediary (usually a bot). A multisig system is used here, in which the signature of the other person is required. It is usually a large company.
This company will sign you the first transaction, but will not sign you a double spend.
Such a wallet is Green Wallet, which has such an option, although I don't know if someone accepts such 0-confs (but there is a possibility). It requires trust in an intermediary, so it's no good.
You can also accept 0-conf, but you should increase the price of this service - to compensate for any losses.
Why did he make such a movie?
I don't know, it's possible that he wants to attract customers (as I understand from bitcoinbch.com - he sells various services to BCH) who are now in Bitcoin.
About Double Spends: https://en.bitcoin.it/wiki/Irreversible_Transactions