To those that play subeku, I wanted to get your thoughts on how hard the 'Hard' difficulty is?

it all depends on how you define hard. I play sudoku in the newspaper and I would say Subeku on Hard is somewhere about Medium in published Sudoku.

It takes me about 5-7 minutes to play Subeku on Hard which is much faster than I can play the published versions.

agreed - it's not overly difficult (just wanted some third party confirmation hahaha) What's strange though is that subeku on Hard vs subeku on Easy seems to be about the same level of difficulty - usually I find a larger gap between the levels in newspaper sudoku.

the main difference, I think is just the hints. In hard you don't get any. But then I've never found the hints to be all that helpful because the hints aren't necessarily correct. I'm really not sure how its programmed, but I do know the hints are based on what's already on the board, even if there are errors.

i've never used the hints hahahaha i guess that's why i didn't notice the difference

make use of the "notes" feature. Start at 1 and fill in ALL notes, then go all the way to 9, then start over.