The minor hassle with the traditional division symbol is that it requires up to 3 taps -- numbers key, then symbols key, then tap the division key. The forward slash is typically readily available after tapping the numbers key, or long-pressing "m" as suggested by Laura Knotek.
It might matter what the reason for typing out the division sign is -- if it's to do the actual operation (i.e, you want to know what 10 divided by 5 is), then 10/5 is slightly faster to type than 10÷5. But if you want that specific division symbol to appear for appearance's sake, then now you know how.