Well, as others have said in this thread, Google or DuckDuckGo absolutely have a place if you’re trying to find a specific thing. DEVONagent is more of a research tool; the key features are the ability to create search sets (of sites and search engines, including custom plugins); the filtering of results (to weed out the ads, garbage, and duplicates, and allow interactive ranking on the fly); the collection of all relevant results in a single live view rather than a series of pages, with auto-generated and generally very effective summaries; and the collection of all results and summaries in a single saveable document with live links.
If you’re looking for a Nepalese restaurant within two miles, Google’s your guy; but if you want to find out about Chinese narratology, DEVONagent will find, sort, and summarise everything you need to know that’s out there, and save the whole thing in a compact RTF file you can then work with in anything, including – indeed, especially – DEVONthink. (You can also save the complete search results offline if you want, though I usually find that overkill.)