I bought a BF-3 a year or so ago and despite having always HATED flangers, have gotten along with it very well. Despite also liking the old BF-2, the extra modes on the BF-3 won me over.
The standard mode sounds good, it just sounds like a normal flanger as you would expect it to. With the Resonance, Depth, Manual and Rate controls you can create pretty much any flanging sound that you want. The Ultra mode is the standard mode but on steroids - it is much more dramatic and in your face. The Gate/Pan setting is quite a nice touch - you can have the flanging pinging between two outputs, which means that you can have a true stereo effect swirling between two speakers OR you can use it almost like a tremolo, setting the speed of the chop with the rate control, which is what I used it for. The momentary setting is also pretty cool, basically you step on the footswitch and hold it down for as long as you wish to hear the effect - great for dramatic emphasis on short passages or even just single notes. I used that setting with a fast rate and large depth for something similar to an extreme vibrato.
Combine it with an octaver and a fuzz and you can get some really deep, synthy sounds. Truth be told it's no boutique analog dream, but it is a pretty respectable pedal that more than gets the job done. It sounds good with guitar or bass, hence the separate inputs.
I firstly moved over to my phaser instead so it sat untouched for a while in my cupboard and now I'm seeking to compound all my modulation down to a Line 6 M9, so if you do fancy taking a punt on one, I've got one for sale in the classifieds (sorry for the shameless plug).