I wouldn’t call this evil, however: it’s merely demonstrating a technique that you should be aware of, if you’re a privacy-conscious person. It looks like they also provide some resources for avoiding stylometric detection.

We should see it as an opportunity to learn how easy it is to associate different pseudonymous accounts. Nothing drives this point home better than a practical demo.

We can be pretty sure stylometry is used widely by bad actors already and we should not punish people who help to spread the word about these technical possibilities.

I'd way rather have someone tell me "look at all the things I can find out about you" so that I can act accordingly (whatever that means!) rather than what we've mostly actually got, which is companies silently exploiting my data and doing everything they can to mumble reassuring but legally ineffective formulas assuring me that they deeply respect my privacy.

edit: maybe you'd catch some criminals if you tried to match reddit against dark web for example