@PatR &
@Phaedrus will surely contribute...
My 2 Cents:
The Mavic Mini released today in pre-order status... if pre-sales are any indication, they have a new hot item in a new niche market: Ultra Light Ultra Compact. It's the first "Retail" drone under the 250g category that allows it to not be FAA Registered and designed with features normally only found on larger drones: Accurate GPS system, 3 axis Gimbal, Photography useable spec'ed camera, an array of autonomous flight options, able to use a large array of 3rd party apps, exceptional range (up to 4Km), both 2.4 & 5.8Ghz Freq, and reasonable performance & flight duration.
Although not required to register (you may register if desired), the flight requirements pretty much remain consistent to registered aircraft that requires pilot continue to follow flight requirements & rules.
As indicated in the B&H Photo DJI Mavic Mini page: "might just be the perfect bridge between the professional and toy drone market"
To the consumer market, it's setting a new standard. Ultra Compact Light craft with performance & photographic specs reserved for larger drones 1-2 years ago. The Price when considering it's including the current tariffs, is still easily reachable and acceptable by a large percentage of the consumer potential Buyers.
How it affects the Other Drone companies? If they manufacture larger drones, or speciality drones most likely zero effect. If they manufacture low cost drones, then the Mavic Mini will be a strong competitor. Currently there aren't any other small low cost drones with the features or performance of the Mavic Mini.
If you're needing a MFT camera platform, higher grade photography platform, a survey platform, cinema, SAR, etc.. the Mavic Mini won't replace those platforms. If wanting a small unit for the bike trail, lug on a family outing, or to experiment with intro quality before the bigger purchase the Mavic Mini might appeal.
Although in my opinion, their biggest competing "drones" are their own DJI smaller models: Tello, Spark & Mavic Air. The smaller Yuneec models would be threatened too.
To other companies, it signals a small platform can contain higher end specs at a low cost. To compete they'd need to exceed on specification within the same price range below $500. That may be extremely difficult to several companies.
Another recent release; the Skydio 2 is an extremely technological advanced USA manufactured drone that is also marketed at low price in comparison to it's closest competition... if this new category actually has competition with current models. I think the Skydio 2 threatens the drone market competition more than the Mavic Mini.
Like the popularity of the Spark, the Mavic Mini will most likely be an extremely popular and high volume sales model. It'll probably exceed previous models easily. It'll appeal to a wide audience from beginner to Pro.
The below 250g and no requirement to register, although doesn't really effect legal flying requirements will probably increase sales in some fashion as it will be marketed as the 1st Unregistered "full feature" drone.
The company DJI have "created" a new market niche, will advertise & take advantage of it and most likely own the new ultra light ultra compact market as the only product.