The question was about sending assets and preserving privacy, not about speed or security. Most crypto currencies are the very opposite of privacy preserving, unless you really think that having all your transactions on a publicly available ledger in a form that is trivial to link to your real identity is a good way of preserving anonymity? Yes I know Monero exists. I also know that vulnerabilities in its privacy model pop up every couple of months and you still have to convert it back into something you can use to buy useful stuff and pay your taxes. Doing this means you're going to probably have to go through an exchange that adheres to stricter KYC rules than the average bank. So again, not exactly good for preserving privacy. Obviously as assets they have massive disadvantages due to their volatility. And given the frequency of hacks and people losing their keys due to general idiocy I wouldn't exactly call most crypto "secure". I'd actually say that the irreversibility of transactions makes it insecure by design.

Personally if I want to send money quickly and securely, be it within the UK or internationally, I use the banking system. It's cheaper, its faster, its more secure and if someone makes a mistake it is easily reversible. I even send a monthly remittance to Madagascar for free, and its not exactly known for its advanced banking system what with it being the 4th poorest country in the world. Yes it takes 2 to 4 days to get there, but I can pay anyone within the EU instantly or if its an American there's always paypal.

I'm 90% sure at this point that the main reason that cryptocurrencies became so popular (apart from the opportunities for massive fraud and bilking of the gullible) is because the USA has a banking system that has barely evolved since the 1980s. I mean they were still flying cheques around in 2004 and I still have American businesses trying to pay me by cheque on a regular basis in 2022. When you consider it through that lens it's no wonder Bitcoin sounds like a good idea.

Monero, zcash, aztec, tornado cash all work pretty well. Could you link to Monero's current vulnerabilities? There have been some known and theoretical issues with the privacy of Monero and Tornado Cash but it isn't a monthly occurrence. How are any of these protocols less secure than sending dollar bills in an envelope?

Sending money with a UK bank or PayPal is the opposite of privacy preserving. The convenience of it is fine for UK to UK and EU banks, not great for private, secure, instant and international payments.