Be careful. Sound Pro's (and most other) battery boxes with roll offs are calibrated for 10 K Ohm input impedance (Sony MiniDisc mic in). If your recorder's impedance is not 10 K Ohms, you will not get the roll off that Sound Pros lists. If your impedance is more than that (and it probably is), you will get less roll off than expected (possibly much less). In the rare case that your impedance is less than 10 K Ohms (Sony DAT mic in) you will get more roll off than expected.
As far as I know, among the inexpensive battery boxes & preamps that we use (SP, Microphone Madness, Church Audio) only Chris Church's Preamps have a roll off that doesn't depend on your recorder's impedance (although you can't adjust the amount of roll off you get with Church gear).
Most of us, I think, recommend not using an roll off when making a recording because doing it this way is not reversible. You can do it is post if desired.