Author of the article here. Let me know if you have any questions or feedback.

One bit of advice left out is very handy: define operators in terms of their inverse.

For example, if I have a != and an == for comparing vectors (terrible, terrible, I know, but it serves as a useful case study), I should only implement one (probably ==), and define the other as simply !(==). This helps make sure that bugfixes to one operator automatically apply to its complement.