All they do is taking Wikipedia's hard work and making money out of it (which Wikipedia has always refused). Everyone's free to make money if done legally but that's a rude way of doing it (since Wikipedia lives from donations). My old laptop can't run it since Wikiwand is so modern. My last concern is that when the addon has been installed, even if you go to Wikipedia you'll be redirected
Btw, the sidebar doesnt work properly on pages with a lot of headers https://www.wikiwand.com/en/Collatz_conjecture