The Boomstick Bottom Feeder is a clone of the old 440 but its amazing, it's my personal fav filter, it's small, true bypass, has a massive range of sounds and is just so musical which is the main thing, a lot of people buy it then think it's subtle but get it in a band situation and its amazing because that huge wetness that other filters might have just sounds like drop out live. 
 
The FX25b is horrible, simply horrible complete and utter waste of time. 
 
The FX25 is cool but very much a 2 trick pony with a maximum of 2 settings one just being a big dubby low pass filter. But generally it's just to unpredictable to use usefully. 
 
So in my opinion just to give you a good idea of what I think the Boomstick Bottom Feeder is better than are 
Moog Low Pass Filter 
Emma Discumbobulator 
Xotic Bass Robotalk 
EHX Bassballs 
EHX Q-tron Mini, Normal, Plus 
Boss AW-2 
Guyatone BR-2 
EBS Bass IQ 
Digitech BSW 
DOD FX25B, FX25 
MXR Bass Auto Q 
 
I've owned or used all of these and end of the day only thing I found that sounds better than the Bottom Feeder is an Original Mutron III or a similar period Mutron Clone but these are like 6 times the size and very difficult to power as Higgie will tell you, also alot of the parts in them degrade so you can't always get a decent one for you £300-£450 
 
So visit www.tonefactor.com and check it out