Earlier quoted context omitted.
I guess for many movements, it's possible to switch to a one-sided equivalent and use the other hand for an easier reset. Barbell press -> dumbbell press
Right, but the article says: "you may be able to cut your weights routine in half and still see the same results." If you do one-arm lowering and two-arm raising curls, you'll have to repeat it for the other arm. So instead of getting "less gym time" as the title says, it seems to me like it will take twice as long, though you will also be doing twice the "up" reps. Maybe that's where the extra gains come from! :-)
Many movements have other ways to cheat the concentric using momentum though. For example with a bicep curl you can swing the weight up to the top, and then doing a controlled eccentric motion. On a pull up or dip you could jump up to the top.
That would allow you to use more weight than you could comfortably use in a concentric motion, to give you the extra loading on the eccentric portion - which may give you better strength gains - without having to do unilateral movements.