Is the fit on the Firearrow 1 2 and 3 the same? Is the only difference the flex?
Yes they are all built on a 100mm last, so the fit is going to be the same in terms of width. The key difference is the flex rating changes from the 1 to the 2 to the 3. They also have different liners. The 1 having the most performance based liner (i.e. less foam).
There are differences between the F1, F2 and F3 (i.e. besides stiffness). The F1 has a different (firmer) liner than the F2 and F3. Also, the F1 and F2 have a wider power band than the F3.