I have a terrible hatred for this band-aid of a tone destroyer. So many people are sucked into this gimmick, thinking it improves their tone.
All it is, is an EQ-ing tool that masks bad tone.
I strongly believe, that a great amp will help you sound great. A great amp will also have all the tone-shaping and tweaking EQ controls you'll need, if you know what you are listening for and know what frequencies to dial in/out. If you buy a mediocre amp, you won't be able to dial in what your ears hear, and then you go looking for solutions. Too many people go buy a BBE sonic crapimizer instead of buying a BETTER amp. They rely on the BBE unit to brighten their highs, add thunder to their lows, change the voicing of their tone.... and then blow speakers or other damaging problems because that BBE does things the power section of their amp can't handle.
If you need a ton of bells and whistles to get your bass tone sounding good, you have a crap amp in the first place and you're masking the initial problem. Outboard 31-band EQ's and BBE's and stomp-box EQ's are just band-aids stuck over a broken leg. It ain't the right solution.
I have so many n00b salesmen (especially at Guitarded Center) trying to sling that garbage at me. I was sitting down with a bass I liked, my brother listening as he just got done looking at what he needed. I was playing through an Ampeg B2RE (that's all they had HOOKED UP, Christ I'd never be able to work at a GC the way they never upkeep their gear) into a 410HLF. It was sounding horrible.
The twerp salesman comes over, "How do you like it?"
I answered, "It'd be better if this amp's tone didn't suck."
"You know what YOU need? A BBE Sonic Maximizer!" he replied with a huge stupid smile on his face, practically bouncing as he mentioned it.
"YOU'RE CRAZY!" my brother instantly snapped, "That's the worst piece of gimmicked crap I've ever seen!"
"Y-yeah, that's why I sold mine!" with the same stupid smile and a timid I-got-schooled tone to his voice.
Face (guy we know from another band and works in guitars) heard us and later shook our hands for not being stupid and putting the n00b in his place. "Total crap, man. They're wheel chocks."
Sorry if I seem to have a strong opinion about these BBE's. But I know crap when I step in it. And don't use the "I can't afford a great amp!" answer with me. If you can't afford it, SAVE YOUR MONEY. Wait until you CAN afford a great amp, then go shopping. Don't take a Crate to a gig and wonder why everyone complains, just cuz you could afford the Crate. Save up, so you can save money in the long run instead of buying band-aids the rest of your musical career.