Chiming in as someone who owns a pro3 and previously owned a mb2s.
The mb2s is probably better at fully integrating into a modular system than the pro3. Great patchbay, fantastic sequencer, can just be switched into different modes to work with different modular paradigms (v/oct, hz/v, etc), it also just physically feels more like a modular synths because you’re using lots of patch cables. However as a stand-alone synthesizer there’s no comparison. The pro3 is many, many times more powerful and versatile. It’s a whole other tier of synth but that comes at a premium. A used pro3 is what, four times the price of a used mb2s? I think it’s more than four times the synth, if not four times the sequencer of modular hub. Either way looking too closely at synths through the price to feature lens makes me feel like I’m at the butchers buying by the pound.
And don’t get me wrong, I love the mb2s. I often miss mine and if I see one for the right deal at the right time I’d buy one again. It’s simple and fun and fast and plays well with others. They’re both great. The pro3 fits me better but nothing is for everyone.
I don’t know if anyone has posted this sound set demo before, but these are phenomenal.
ok…
I sold my A4m2 and got a Pro 3 SE yesterday. I didn’t want to go to bed because I wanted to play with thing until the sun came up.
I’ve had a lot of synths, but this is truely the first one that has captured me.
Although I will definitely say that the A4’s sequencer is the pinnacle of sequencer+synth in a box, and that the Pro 3 has just a taste of the A4’s capabilities, DAMN the sound from the Pro 3 is delicious!
I may end up with an A4m1 down the road, but I truely think the Pro 3 is a keeper for life. It’s capabilities truly are endless and it sounds AMAZING.
exactly how i feel about it. the A4 was too much sequencer and not enough synth for me; this is more synth but still with a really, really good sequencer. the the Pro 3 user experience is just phenomenal imo - you can get SO much done without referring to the manual. so intuitive
I’m with you in this one 
And me three. Best mono I’ve had my hands on.
I had some good synthesizer fortune a few weeks back. I ordered the normal version and they sent me the SE by mistake. The Pro 3 is the best synth I’ve ever had. The only other that’s come close is the Hydrasynth, which has similarly capable mod matrix. I’m in love. And I haven’t even gotten into the sequencer yet.
haha that’s a win!
Another dope demo:
So many of these YT vids focus on the distortion/feedback side of the Pro 3, but to my ears make it sound thin and brittle easily… this one shows the fidelity range nicely.
So… could be just the glazed-over honeymoon phase/confirmation bias talking, but this might be the best sounding synth I’ve ever heard.
I’ve had it over a year and feel the same way.
It’s like all the best things about the Pro 2 and AS-1 in one synth… well, almost anyway. A sound designer’s dream.
Sometimes just a single raw saw wave will make my mouth water. It’s truly a magical synth.
Damn, you guys have me wanting to pick one up just so that I can dip it in ranch.
Tasty 
Does anyone know if the track lengths within a sequence can be set independently (ala Elektron?) Not seeing this in the manual…
Yes! I’ve done it in the past. Lots of fun!
Perfect.
Posted here: To change the length of a track after recording, press ‘reset’ while holding down the step button of whichever step you want to be the final one for that track. The letter R will appear in the next step along.
Exactly what I wanted to know. If they added conditions and/or probability it would be very close to Elektron.
Besides all the ways that ability could be used to modulate the internal synth parameters in interesting ways, having 4 independent-length cv sequencing lanes (plus gate!) out to modular gear is super dope 
A related question… when sequencing in paraphonic mode, can each Osc/note track be set to it’s own length as well?