I haven't done a transfer myself because I had an Android break before my current iPhone 12 Pro Max. But from acquentainces that have done, they are happy with. Remember that it has to be supported by your provider too. EE support it and according to Apple
https://support.apple.com/en-gb/HT209096 only EE do in the UK.
With O2 and Vodafone you will need to find alternative ways of activation. Although Vodafone do online issue of eSIM from their website. Three mention it on their website, but do not issue new eSIMs indefinitely.