I just installed the Itty Bitty Double Flex, flashed the firmware for it, did M502 followed by M500.
All of my prints seem to have about ten times too much PLA extruded.
I have attached a picture of the 2mm spacer that I printed before installing the Itty Bitty Double Flex, and one that I tried to print immediately after. I used the same GCode file in both prints.Attachment 8436