I love Modulargrid, and at least for my use the features it has are very intuitive and "just right" in the way that is rare in a tool.
The only niggle for me is the keyboard shortcuts. I don't know why, maybe it's because I use Safari, but relatively often (at least a couple of times per an evening of binge planning racks) they bug out in some way. Clicking the module search box does not always seem to correctly move focus to it, and when I type the module name, random keyboard shortcuts are triggered instead and my rack goes bonkers with modules deleted or duplicated. This is very infuriating especially with a more complex rack, where it's not always easy to tell what was changed.
Whenever this happens, the only consistent way of getting rid of this bug is by refreshing the page completely, and even then I still have to fix the changes to the rack design itself. I don't feel I even need the keyboard shortcuts, and they are rarely used on websites anyway because of problems managing focus – not a problem if you have a single HTML5 canvas and the focus sticks to that, but mixing HTML elements with keypress catching is something I would personally avoid. But that is of course for you to decide, and apparently many people use the shortcuts happily and without any problems.
I think the easiest solution for people who have this problem would be to have an extra checkbox in the profile settings to simply disable keyboard shortcuts entirely.
Thank you! :)