Well if you're talking about stuff that's used at physical checkout counters, you need really fast transactions. Nobody wants to sit there for an extra 20-30 s

Well if you're talking about stuff that's used at physical checkout counters, you need really fast transactions. Nobody wants to sit there for an extra 20-30 seconds holding up the line. Even if customers can tolerate it, businesses will be much less inclined to support such a feature.