Speaking for myself, I'm deafblind and don't need a pair of glasses or vibrating shoes to warn me about obstacles, stairs, etc. My guide dog or white cane (and my own two feet for that matter) do that just fine from a longer distance than 2 inches.
GPS technology is already available to the blind and deafblind via the BrailleNote and PacMate (PDAs for the blind).
These shoes can't be used in the snow or rain which means they would have serious limitations for blind people who live in such climates.