Don't like it..
Besides the fact that discs really suck (sorry, but lets be honest, they really do), and nobody ever kills anything but a noob with it (or someone caught of guard) this idea just wouldn't work..
Someone visible, not behind a mountain or something would get fried in an instant when controling a disc.. ESF maps are big, but not THAT big..
And i don't feel like searching the map for somebody hidden behind a tree or rock or something because all these controlable freeza discs are constantly flying around..
And besides that, if i see somebody charge a disc, i'll teleport to the side and just throw 1 ki-blast in his direction and he'll lose control.. or choose to "leave the disc mode" and evade thus losing the disc..
So the attack would only be useable if nobody has seen you in the first place..
A homing disc would sound better to me.. high turning speed, high speed and wich automatically follows your opponent around..
As long as the disc is active, it will slowly deplete your KI bar.. it will disolve when you have no more ki, of after 15 seconds.. (This time would get increase along with your transformations)
When the KI pool increases, or a certain level is reached, there would be the ability to charge use 2 discs at once..
While using the disc, movement would be restricted to jumping and walking around and you would not be able to charge ki.. so opponents can still try to slice you up with your own disc..