I have the size 12/13 for a size 12  Asics running shoe.  Perfect fit with nothing to trim.  I am a size 12 narrow, medium arch with a fairly thin foot.  This insert is not much thicker than the original, except for the arch support area which is MUCH thicker.  So much thicker that it took some getting used to.  Very different feel than the Spenco Walker Runner and Cross Trainer inserts and a much better choice for running. It also weighs almost 50% less.  45 grams per insert vs. 85 grams for the Walker Runner.

Modest cushioning compared to the Walker Runner and Cross Trainer but my feet like these better.  No stability issues either.  The heel section on the Cross Trainer is so thick that it makes my running shoes unstable. My foot wobbles on top of the insert rather than cradled in it. Very easy to roll your ankle with the Cross Trainer (which I did).  And trying to run on an insert that has my heel jacked up forces my foot and ankle through an unnatural range of motion creating  orthopedic issues.

Spenco claims this insert keeps your feet cooler than other inserts.  I could not verify that claim but I have had no issues with heat build up.

Bottom line, the Flow feels natural and fluid to me and I like it.

Recommended.