HN's UI gives you a much stronger hint of what the controls do.

You cannot undo an upvote (you can unflag posts and articles though). This is particularly a problem when using HN on mobile devices where distinguishing up and down votes is all but impossible. I'll often make multiple wrong clicks trying to navigate to a link or vote on an item. It's frustrating.

Subtle's interface is doubly deceptive: it lies to the user and it misrepresents the consequences of those lies. Makes me lose a lot of trust and faith in the product, actually. As well as those who use it.

Funny how things brand you.

HN doesn’t let you un-upvote something either, but you need to un-upvote something on HN far less often than on Svbtle. On Svbtle, it is very easy to accidentally “kudos” a post, because all you have to do is move your mouse over the kudos circle, and the site doesn’t warn you that doing so will trigger a kudos. On HN, at least you have to click a button-looking thing to trigger the non-undoable action of upvoting.