Personally I think locking blades are an important safety feature and should be on all knives.
Sadly the UK legal system (due to one Judges ruling many years ago) seems to think locking knives are inherently more dangerous to the general public. As a result they are banned in a public place unless with very good reason, which is normally dismissed.
There is a way in which to stop a blade closing without a catch and that is to design it in such a way that the users grip on the knife prevents accidental closure. It’s often not particularly elegant and I doubt it would work for a SAK.