This is a great idea, as are containers generally: isolation much like virtual machines, but a level higher (above OS) so with much less overhead.

This particular app works well but is frustrating in one respect: you cannot specify to open a site in container X in future without already having done so. As it is, you must first re-open your site in a preferred container, then choose to always do so as a second (manual) step.

Even so, this app provides cross-site isolation. I feel much better having all my banking in a container no other apps see.

I accept Facebook tracking my tastes & movements as a fair exchange. If you don't, use the Facebook Container app but get this one anyway, for everything else.