A friend (the one with the PA3X, G70 and G1000/600) just got a BK-3 and dumped it on me for a day... I'll probably have a bit more time on it soon.
Overall, for a roughly $600-$700 arranger, it ain't half bad. Light as a feather, stiff as a board, layout is pretty good. Most of what you want where you want it. No battery operation (external lump in the middle PSU) sadly.
Only one UPR and one LWR Part, or a full layer (or an Upper only layer), about average for the price point. Rev, Chorus, and 2 MFX insert effects, freely assignable between Keyboard or Style/SMF Parts. That's pretty good...
The sound is pure Roland... live sounding, with plenty dynamic drums, good basslines and a much improved (from the G70) set of guitar parts.
Is it a Tyros? LOL no! but you can buy 8 of these for what a Tyros costs!
It does have the wonderful Roland Makeup Tools for editing styles and SMF's, by far the best and easiest style/SMF header and drum kit editing tool of all, albeit, it's a bit more navigation heavy without a nice big touch-screen. But being able to adjust velocities AND volumes for not only full parts, but for each drum sound within a kit goes a LONG way to being able to squeeze the best out of legacy styles and SMF's.
Speaking of which, my friend is married to some quite old Roland styles he still swears by, and direct from the USB stick, no editing, they played very well, albeit with the original drumkits and sounds (mostly - when the exact same sound wasn't there, the closest equivalent is substituted). So he's good to go even if he doesn't avail himself of the Makeup Tools.
It has both USB stick input, AND 'To Computer' ports, and a wireless adapter is available (extra) you can use to send lyrics to an iPad or iPhone for display.
Overall, although I didn't set up a direct A/B to my BK-7m (I'll do that next time I get it) I felt that some of the sounds felt a little less full... usually, budget arrangers try to squeeze their sounds into less ROM than their more expensive siblings, so samples sounded a hair 'grainier' or went into their loop earlier than one might want, but again, a $600+ arranger should not be expected to be EXACTLY the same as something $4-500 more!
I'll get into it a bit more when I get it next... It DOES have much more extensive 'Hold' parameters than the BK-7m did when it came out (an update addressed some of this on the BK-7m), and seems pretty easy to run from the front panel. There are a LOT of 'shortcut' button pushes (press and hold the tap tempo button to 'lock' tempo, for instance) and sounds and Performances can be called up numerically, as well as from a Performance list of 999 setups per load.
More to come...
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An arranger is just a tool. What matters is what you build with it..!