It's best to use Draft on your laptop with a Chrome Browser for now. We have future plans for app, but we don't have specific date for the moment.
You can also use it e a big touch screen like the Surface Hub: it adapts automatically to touch hardwares and we have a fairly good experience on these devices.
We're getting much more productive with tablets and smartphones but we're not quite there yet. But we are working on it. Reach us here
if you want to get updated.