Let’s try a metaphor. Say I have a bike. Someone’s trying to sell me another bike, based on it having two wheels, both compatible with standard tubes, and optionally having a luggage rack, if I bring my own and attach it. Then I would also be asking them what their bike actually does and why I should bother swapping mine out for theirs, because it just looks like an extremely standard bike. It doesn’t mean I do not know what a bike is.

The question about lawnchair specifically has mostly been answered by comments now, but the website still does a very poor job explaining what it does over any other launcher, especially compared to the stock one.