Most estate plans fail for lack of funding. Most online, and even some simple trusts, leave the funding up to you. Unless your assets are transferred into the trust, the assets go to probate court and the lengthy and expensive processes that the court controls, not you.
Thus, DIY while appearing inexpensive may cost your family tens or hundreds of thousands of dollars. Is this a risk you are willing to take with your hard-earned wealth? Will you leave your children a mess that will take years to untangle?