1) The most dangerous obstacles are not at head level. Furniture and most of the other things that can be tripped over and stubbed on are waist level or lower.
2) Vibrating motors stuck on your skull will drive you insane quickly.
In addition it would be a challenge to disguise it as anything but some mad-science-looking headband, and blind people do care how they look.
Also check out the man who learned to echolocate http://www.mensjournal.com/the-blind-man-who-taught-himself-to-see
I've written about "super" senses and sensory modification before... I'd love to actually look at the neuroscience behind this kind of extra-sensory modification.
A blind guy I know is very interested in this project/product, and has apparently been pleased with the phone app. I can't tell if it's still a shame that there's no dedicated Walkman-type appliance - smartphones are finally cheap and prevalent, but battery life has got to suck and finding and interfacing a head-mounted camera for more regular 'vision' is still a nightmare this week.
The specific software also seems to suffer from serious creeping-featuritis, but his attitude seems to be much more "Like I have something better to do than learn how to use all this awesome stuff?" (As someone with working eyeballs, I'm pretty sure I'd want something more reliable and less modal if they suddenly blew out one day, at least for the first dozen months.)