OP1 and Octatrack are, like, polar opposites. Both are beautiful devices weighed down somewhat by their idiosyncratic interfaces: OT is like a piece of industrial automation software from 1999, OP1 is like an iPad app. OT is great if you like excrutiatingly building the framework of a machine and then reusing it a bunch in new contexts. OP1 is best for noodling and cut-up technique work IMHO.
In the end I sold both devices. OP1 doesn’t play well with others (awful MIDI implementation, bad audio output) and OT is too slow a workflow (and it’s not as portable). I have been much happier with the ER-301 in a tiny pod for my loop/sample/mixing needs.