The POST workaround does not work for some websites, mostly forums-type websites, wherein the search result URL does not show the text that was searched for OR if it has a random string generated in the URL along with the text, which changes with very search (kinda like a unique search ID).

Other than that, its very intuitive to use and easy to add search engines to once you create the "Searches" bookmark folder. Can't get simpler than this.

Its just for the lack of POST support that I am forced to use another extension called "ContextSearch web-ext", even though it is way more complex to set up and use than this one.