You can benefit from a BFD but the GREATEST benefit is in EQing the midband response - if and only if you have point source speakers (conventional electrodynamic 2 way/3 way). For bass you can calm down a sharp resonance if it is troublesome, but subtle improvements to LF response are seldom heard. Problems in this area are best solved with passive absorbers such as the ones from RealTraps because the ones from RealTraps don't absorb MF/HF energy.
Sometimes only one frequency is a problem and other than that bass is fine. In this case an EQ may be the answer.
If you are a home theater fan and you listen to lots of dialog, subtle improvements in the midrange response will be immediately heard and greatly appreciated. Human hearing is most sensitive between 100 Hz and 5 KHz. Midnad drivers often have problems around 2-4 KHz because of cavity resonances and sometimes poorly damped cone breakup.
The RS SPL meter is great, but only suitable for bass and measuring room reflections.
The Behringer equalizers are excellent and very well made. If they were strictly a high end audio product, I could see them charging thousands but almost every live sound man has one so volume drives prices down.