So I’ve happily owned a TD3 for some time (best bit of Behringher kit I’ve owned), but recently upgraded to an RE303. I bought parts to build one a few years ago but then had a kid, decided it was never going to happen, and eventually had it made by Kumptronics.
First off, I’m genuinely surprised how much better it sounds than the TD3. I thought it might sound a bit better, mostly wanted it for geek reasons, but the difference is night and day. It just sounds so much more loose and liquidy. I’m fairly certain it’s not just cognitive bias 
Purpose of this post however is this: in the couple of jams I’ve had since getting it I’ve had tuning issues. Immediately I was certain that it sounded better on the pure acid stuff, but when I jammed with it on my more melodic tracks it sounded off. Checked the tuning and it was bang on, so really confused. Eventually after much frustration I checked the tuning on my TD3 and realised that it is tuned to B instead of C when the tuning pot is at centre. Nice one Behringher! The nuts thing is all my 303 patterns sound in tune with the 303 mistuned, so I’ve wound up tuning the RE303 a semitone down, and now the RE303 works with my melodic tracks. My music theory is pretty average, standard for an electronic musician with no formal training I guess, but I’ve generally got a good ear (although clearly I missed that the TD3 has been out this whole time). I don’t really get how it is that it sounds so right when some really melodic 303 patterns are essentially out of key the whole time. I’m not really after an answer to a question so much as just voicing my general confusion. I’m happy for this to be one of those happy accidents that contributes to ‘my sound’, I just hope that actually knowing about the mistuning won’t affect how I write patterns in the future!