There’s a mis-conception that all SARON mortgages are fully flexible and repayable at any time. I was surprised to find this was not the case and some banks give you the SARON rate, but still impose a mortage term e.g. 5 year, 10 year etc. during which cancellation has the same kind of penalties as for a fixed mortgage. Do read the small print!
If you have very low long fixed rate mortgage, it is an asset and is easy to deal with as you’ll sell and transfer the mortgage to the buyer.