If you have the Inserter Overhaul in Logistics mod turned on, it removes the "Long handed inserter" item/entity/recipe.
Instead, the research adds a button to the "Top GUI", which if you're not using a whole heap of other mods, is basically the top left corner of the screen. The button has a picture of a fast inserter on it. This lets you turn on an override where you can choose "Long reach" or not. if you check both options, then when you place an inserter, a script will change it to be longhanded. ANY inserter, Burner/normal/fast/express/turbo/ultimate, in any varient, filter/stack/stack filter.
If you also have the Inserters mod installed, then the button exists in the top left corner to begin with, unlocking the technology adds the option just as before, and when you use the GUI (There's a GUI mode option in the menu that opens when you press the button for choosing hand positions pre-place, but also if you click on an already placed inserter, it opens a GUI that lets you choose hand positions, and CTRL+E opens the same GUI in the middle of the screen), you'll notice that before the research, you'll only have the 4 options directly adjacent to the base of the inserter, but if you research Long handed inserters, you'll have the 2 tile reach options available too.
TL;DR:
The default behaviour is to have the "Inserter Overhaul" turned on, so the Long-Handed inserter isn't available, but the research unlocks options to make ANY inserter Long-handed.
