beat step pro is way more immediate. you patch cables and jam. you will still have to tune your oscillators or whatever but for drum stuff the beat step pro couldn’t be simpler.
the thing the dubledecca gives you is all the modulation ability of the OT. you have to set up the template (there’s instructions for that in the dubldecca build manual) btu you will be able to send the LFOs and stuff out of the OT to use as modulators in your modular. you will be able to send trigs, clock, pitch etc via the dubldeca and save…
beat step pro also allows for saving patterns. and has CV outs for step relevant CV control.
it really just depends on how you want to work… and if you want to use the OT as a center piece for your modular. you get al the OT has to offer… independent track lengths, different clock divisions per track, micro timing etc…
i’d recommend watching a bunch of beat step pro demos and tutorials and seeing what makes more sense to you.
beat step pro is inexpensive and very capable