If you are using a direct fired MLT, then go with a false bottom that fits the bottom of the MLT. I think you would nhave a higher probability of scorching your grains using a bazooka screen as there is no dead space between the flame and grain. Also, your efficiency will be low using a bazooka screen. I do not know if a bazooka screen would be able to accomodate the weight of grain required for 15 gallon batches without crushing itself.
Since you spent the money on this shiny new equipment, get the false bottom to get the most out of your money.
Thats my 2 cents.