RSUs and ESPP are actually two very different things. By default, anything of value your employer gives you is considered compensation, taxed at ordinary rates. RSUs fall into this category.
But there is something called "statutory stock options", of which there are two types: ISOs and ESPP. The main benefit (under statute) is that if you hold on long enough, instead of ordinary compensation income, the gains can be treated as long term capital gains (LTCG) and taxed at a significantly lower rate.
To be fair I never claimed they were the same, just that my "simple" advice applies equally to both. I only called out 2 examples of the many ways this article is lacking in nuance on the details.
But there is something called "statutory stock options", of which there are two types: ISOs and ESPP. The main benefit (under statute) is that if you hold on long enough, instead of ordinary compensation income, the gains can be treated as long term capital gains (LTCG) and taxed at a significantly lower rate.