It's as comfortable as anything else created out of the same materials. Without extensive post-processing, fully printed converse shoes, even with thin layer heights, would almost certainly result in chafing.
3D printing isn't the Star Trek extraterrestrial technology that some people believe it is; it's basically CNC technology from the 1950s or 1960s combined with a hot glue gun that squirts plastic layer after layer.
Don't get me wrong: it's cool and useful, but it's not extraterrestrial technology built of elements that don't appear on our periodic table.