Upload & Sell: On
On one end of the spectrum ... you have gadgets and adapters to try and find a universal & cheap way to achieve a given objective.
On the other end, you have OEM with a dedicated line of accessories.
Many talented individuals have touted their ability to use either to produce their desired results. But, what can be a varying factor is the amount of time they invest into setup, how infrequent / frequent they change their setup, the frustration they incur, the longevity / durability of the product, or the system compatibility.
I realize that this doesn't directly answer your question @ "light output is obviously superior". But, to that point, I'd suggest that as you move from the more simple light shaping modifiers like umbrellas to more complex designs like beauty dish and parabolics, the differences can become a bit more pronounced at hot spots, etc.
That being said ... my latest issue with third party modifiers is a grid that I'm having to "clamp in place" so it doesn't fall out when using it pointing straight down. The designed retaining clips work like a champ for "normal" use ... but, "Uh-Oh" when using at "extreme angles" and the grid starts to fall out on your subject as you are positioning your light.
Sure, there are plenty of options to choose from and some good third party products ... but like most things, "There is no free lunch." & "You get what you pay for." ... whether it be OEM or third party.
IMO, it is somewhat like asking if Grandma needs to spend the money for a Hummer or a Hyundai when she wants to get a new SUV ... depends if she's hauling her groceries three blocks from Wal-Mart or she's headed to Canyon de Chelly. Fit for purpose has its bearing as well.