Like all logia type devil fruits the main ability of Reddo Reddo no Mi is to tranfsorm into lead, create lead or control lead. The user can only control, create and transform into liqiud, solid or liqiud-solid lead.
Being able to transform into one of the heaviest and most unhealthy metal, one can easly drown an enemy in lead so the enemy will suffocate. The consumer won't realy gain much strength from the fruit.
Another ability (it's more an side-effect) is to use the lead onto a person so he or she will get brain problems, like becomming senile or lose the ability to function well. This ability isn't the fastest kind of attack since it takes atleast 20 minutes before the enemy's brains starts to fail.The lead can also damage nature by poisonning the water, plants and other sources of food.
Besides the standard devil fruit weaknesses, there aren't any known.
It's unknown how the devil fruit looks like.