It would be okay if I typed in facebook.com or faecbook.com, sure. But not allowing me to see the index for "facebook" is really not what I expect from a search engine. What if I want to type "facebook" and see general information, or news? I can't as your search redirects me away.
Maybe offer a card: "Do you want to visit Facebook?" would suit the best of both worlds. Or, if you must, a 10-second auto redirect.
from my anecdotal experience: having anything other than a hard redirect entirely misses the point of this feature. A click or waiting 10 seconds pretty much nullifies all the benefit. I think an opt-out is the best way to go. Any technical enough user that is bothered by it should be competent enough to disable it or be aware what happens when they are trying to get general information.
Observing my dad using his iPad, he regularly types sites without the TLD with his only intention being to get over to facebook.com
How often do you search for just "facebook" (or any other site) without any other qualifiers and expect to get information or news? If you search for "facebook" on Google all of the results above the fold just go to facebook.com page anyway. If you want info about the most recent facebook scandal you'll likely get better results from any search engine if you add more search terms e.g. "facebook scandal"
Maybe offer a card: "Do you want to visit Facebook?" would suit the best of both worlds. Or, if you must, a 10-second auto redirect.
Anything but going straight to FB.