There are a ton of replies with counter-examples, but all of those are not exactly like the OP-1: a fun, easy to use, ultraportable, immediate music creation sketchpad.
Many other grooveboxes are quite painful to use. Here I’d include the Korg Electribe which is terrible at inputting musical notes. Or the several trackers which look more like scientific calculators than musical instruments.
My MPC live can run circles around most grooveboxes, the OP-1 included, but that’s because it’s a computer: quite a bit heavier, takes time to boot, requires you to manage projects and adjust many parameters.
The Model Cycles doesn’t have a battery. Can be powered by a portable one, but that makes it just a little bit awkward. Elektron did launch a handle battery but it tended to catch fire in rare circumstances :-) Elektron boxes are in general considered difficult to use, even if the results can be impressive.
The Novation Circuit doesn’t allow full editing of the synth parameters. The synth parts are more like preset editors. Expect having to manage them from a computer.
The Deluge has a cumbersome buying process, where one has to basically buy from the manufacturer (NZ I think). I actually can’t but it from my/any local store. In reviews I’ve read that the interface is not that user-friendly/immediate.
Then there’a the multi-device set-ups consisting of Volcas, Rolands, etc. These can be nice, but it requires wiring them up every time! If I had to wire together 3 devices before I could make music, I’d rather do something else personally.
And so on and so forth. The new OP-1 is overpriced though. Maybe at 1500€ this would make some sense, but at this price point most people would rather deal with the disadvantages of other devices or device combos.