I didn't intend to make any claims about global market penetration. Just pointing out that it has notable tractiom in my market and peer group, and that because of that it had made strides towards the ideal bill-splitting situation outlined above: it is used widely enough that it's a clear default when splitting a bill with a mixed group. Maybe it won't catch on any more widely, but similar apps have been around for a while and never reached the adoption where multiple people in a group would suggest or accept them as payment. It's not actually available outside the US right now, which may be why you haven't heard of it, and which is clearly a big hurdle on the road towards true ubiquity.