I can't say anything for or against the Bullydog kit. However, I do know that there are alot of different things changed on Performance Valvebodies than just a few springs. I know there is some machining that goes on to increase flow and to change shift firmness and control shift points and such. The description of the Bullydog kit is so vague I really don't know what it does besides raise line pressure.
If I had to post a suggestion I would say go with a performance valvebody.
If tyou feel confident in pulling the valvebody apart, then the Bullydog may not be a terrible choice. Maybe someone with experience with Bullydog will chime in.