These are regulated and offer more protection for you as a client. You don’t necessarily have to use a lawyer, but wills are legal documents, meaning they can be invalidated if there are any errors present. It is, therefore, important to make sure it has been correctly drafted.
A lawyer should know the exact process to follow to create a watertight will document. There is, of course, no guarantee that they will do a good job but using a solicitor means you will be more protected if something does go wrong – even if it happens after your death.