alotta old trail bikes had a separate giant offroad sprocket. they'd use 2 master links and you'd just link in the extra length of chain for offroad, or take it out for the topend on-road gearing.
later honda started putting the hi/lo switch inside the motor on the ct90s and 110s so it was a quick easy high/low switch. it think these were just a quicker on/off switcher for the old style, and became pretty much obsolete
it wont work on the fly, it shifts when you're stopped. the bikes it was made for were geared already, and it just was to switch the overall final gear ratios for offroad gearing once you reach the trails or woods.