Size and capacity. The 908 is a single stack thin grip, the 910 is a double stack magazine with a corresponding larger grip. Uppers (slide/barrel) are longer on the 910. Both have an aluminum alloy frame. Their sizes approximate the 3913/5903 dimensions.
908 has a 3 1/2" barrel, the 910 should be 4". Any of the 8 round 3913 mags should fit the 908, but I don't know if the 7 round mags will. The 908 factory sights are a goofy size, I don't know about the 910 sights - replacement sights are limited.
Here is my blued 908, the slide started to rust so I paid to have it hardchromed- this extra money could have paid for the better 3913 model. The stainless 908 should not have this problem.
And before you even ask, yes, the 14 and 15 round magazines will fit and function in the model 910. Think of it as the 5904's less attractive sister. -Ed.