Atom Hidpi scales Atom's interface based on the current monitor's resolution. Currently on Linux Atom does not scale based on DPI, so this package is necessary to make Atom readable on monitors with high resolutions / DPIs. This package should not be necessary for OSX because it automatically scales. I have not tested Atom on Windows so I do not know how it behaves.
By default Atom's interface will be scaled up 2x when it starts up if the current monitor's width is above 2300px. If you move Atom to a different monitor, you can update based on the new resolution by opening the command pallet and calling the "HiDPI: Update" function.
DPI cannot be determined by resolution alone. A 5 inch phone and a 27 inch monitor with similar resolutions will have vastly different DPIs. Because of this, this package's default behavior will not be desirable on multi-monitor setups where the monitors' DPIs vary significantly. Use the "Manual Resolution Scale Factors" setting to assign the appropriate scale factor to your monitors.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.