So being in San Francisco this weekend I encountered yet another version of Uber "Express Pool". It's basically Uber Pool, except a bit cheaper and requires you to relocate to a certain place for the pickup. In both times I've used it I had to move 3-4 blocks, or about 2 minutes of walk time. My experience has been positive but I wonder about the sustainability of the economics. Both of my rides have been about ~$4 that would have been $12-15 if a normal Uber X.

This seems to be limited to San Fran and Boston as test markets, according to the Uber website.