for me the Series 0 through 3 work wonderfully! the bar code on the watch even turns based on how you hold the watch. great experience! Stocard has updated the app already 3 times BUT did not fix the display resolution on the 4 so I am guessing in on the bottom of the list. My health club they lock the track with a scanner as well as the door for the club so it is SO great to use the watch and not have to break your stride...
Ps. I am still waiting for Facebook to update their app for my 2015 12.9 iPad so hopefully Stocard gets to in before that....