ITX 10 is between steel & lead, in performance. ITX 13 is heavier/better than lead performance.
ITX 13 is basically their own version of Hevi-Shot.
I have never used the ITX but have shot lots of HeviShot and straight TSS. If the ITX 13 patterns good (out of your shotgun), it should work great.
I, personally, would not pay the extra for ITX 10 unless I was shooting it out of older, non steel shot approved gun.