I have an OP-1 and an OP-Z. More and more I use the OP-Z, the sequencing workflow is just incredible. I don't have an ios device and after climbing the learning curve it's totally functional without a screen.
Also, the OP-Z can be used to sequence several pieces of external hardware at once [0]. Definitely not a toy. It has it's quirks (e.g. adding your own samples requires chopping them to exactly 6 seconds or all hell breaks loose, and no ability to "zoom in" on your sequence if you have multiple trigs per step) but it's a trade-off for all the power in the form factor.