Two small improvements I would suggest:
1. A sorting order where checked tasks are moved at the bottom, keeping only the unchecked ones on top. (I could not find this if it's already implemented). Note: I want to see all of them, just have the checked ones moved.
2. The save button on task creation is a bit weird. It occupies the top row, together with the delete button on existing tasks, but the checked button is floating on the right. You might want to unify the look of these 3 buttons.
Otherwise, good work! I'll be using it from now on. Normally I'd use Orgzly for tasks, but grocery lists are a bit different, you want to be able to operate them with one hand while carrying your groceries with another. This app allows that while Orgzly is a pain to work with as it requires multiple actions to mark a task done. I know this from personal experience.