Yeah the volume drop is tough. Gotta turn that oct1 all the way up, and only play above the 10th fret or so. It's the one fault of that pedal lol!
Some do a mod to boost the volume of the oct, and I suppose if you ran it in a loop you could boost the vol there as well. I either just go with it as-is, and embrace the slight vol drop (mine isn't that bad if I peg it and play up high) or I run a transparent overdrive after it with a slight gain boost to even it out (but then you're tap dancing two pedals on and off, doesn't bother me but some hate that lol) the transparent drive adds a little dirt and warmth that sounds great with the synthy oct.
As for Flangers, I sometimes use the Boss bf-3 with great results (usually about $50 used on the TB classifieds), but my fav is the tc electronic Vortex flanger. Super flexible. It can be set very subtle, which is how I generally use flange. (although the bf-3 does that swirly oscillator sound extremely well and even has tap-tempo so you can sync up your swirl)
Never tried the behringer, let me know how it works! I have their bass synth pedal and it's pretty ok. A steal for $45 brand new from amazon.
Sorry for the lengthy reply!