DIY Wills are legal. If you have a highly complicated set of requirements or a difficult family situation, it may be best to consult with a lawyer to help you get through the relevant challenges.
Online Wills are typically accepted so long as they've been printed and signed by hand.
Handwritten (holographic) Wills, however, are frequently rejected—even if you have witnesses. GoodTrust's Legal Will and testaments are typed.