I mix on decent headphones and check on bad ones. The bad ones cost about fifteen quid, have no low end to speak of, and are the closest thing I own to how most people will actually hear the track.
What they catch isn’t detail, it’s balance. A vocal that sits perfectly in the good pair will regularly vanish in the cheap pair, and the fix is almost never EQ. It’s that something else is too loud.
They’re also useless below about 100Hz, which is exactly why they’re worth having. If the track still has weight with the bottom octave missing, the arrangement is doing the work rather than the sub.
So the rule I’ve landed on is that a mix isn’t done until it survives all three. Good headphones, cheap ones, and a phone speaker held at arm’s length. Two out of three is a mix that only works somewhere.