I need to talk a bit about the TR-909 first as an introduction. I had the brief opportunity to use a real 909 once, a long time ago. Also my previous experience with the ReBirth software made me feel like I already knew where to touch and what to do.
With the RD-9, the same thing happened, it felt familiar right away. But I also found what, for me, is a fatal flaw in the design. I don’t compose or record audio from the 909. I jam with it alongside songs. And here, the spacing between the knobs is tighter than on the real 909. Touching the toms’ volume knobs, for example, often made me change their tunings by mistake. That sucks when you’re jamming live. My workaround was to remove the tuning knob caps, but I really shouldn’t have to do this. Honestly, I don’t understand why Behringer didn’t go the extra mile to get the spacing right. Maybe it’s my tree-stump fingers, I don’t know, but this never happened to me with the real 909, and I was already a grown man when I jammed with it. You might also think "well.. but you can mute channels in the RD-9!" ....
That's the problem:
As for the interface… it’s not optimized. The extra features Behringer added are nice touches, but there’s absolutely unnecessary menu-diving for certain things that could easily have been solved with button combinations. And no firmware upgrades addressing these issues have appeared, which is a shame. Simple stuff like muting or soloing channels, or even being able to use step triggers more flexibly, feels more cumbersome than it should.
Another strange design choice: when you mute the closed hi-hat, the open hi-hat gets muted as well. The 909 doesn’t have the “extra” hi-hat like the 606 does. On the 606, if you program both open and closed hats, there’s actually a third hybrid sound. The 909 doesn’t work that way, so why muting the closed hat also mutes the open hat is beyond me.
So yeah, button spacing, lack of key combos to avoid menu diving, and this mute/solo issue are really the only cons.
As for sound quality, there are already a million videos comparing the two. But honestly, on my humble setup, I cannot hear the €4500 difference between the RD-9 and a real 909.
Bottom line: you will most definitely enjoy this if you’re looking for fun or want to do some serious work.