DualPistols - Cryo Ammo - what kind of slow?

It's -spd and -rech. Personally, I don't think that it's all that worth it. In order for -rech to be particularly useful, you have to stack a lot of it on a target and that target has to be alive long enough to cycle all of its attacks multiple times. As a Blaster, if a target gets to cycle all of its attacks multiple times, you're normally dead already. If you're not, the target is generally dead by the time it would get to that point.

In all honesty, there really isn't a reason to use Cryo Ammo (beyond simply wanting to shoot ice bullets rather than fire/chem/standard bullets). The debuff isn't particularly useful and the additional damage you would get from dealing a portion of cold damage is less than you would get from simply using Incendiary Ammo (even against enemies like Behemoths that resist fire and are weak to cold; the additional damage from incendiary more than outweighs the increased damage from the cold weakness). On my DP, I only ever used chem (for -dmg) and incendiary (for more damage).

Unless of course, you're DP/Ice...