a DSLR or mirrorless body with a good lens will have much better image quality vs theta or other one shot cameras, but comparing a dual camera/lens device that costs under $400 total vs a $1k+ DSLR (or mirrorless) body & $300+ fisheye lens is not exactly a fair or even comparison, small one shot 360 degree spherical cameras are extremely convenient and very useful for some situations, but larger image sensor are of DSLR + higher quality lens will always beat the quality of an all in one device costing 1/10 of DSLR & lens, an all in one 360 cam that competed w DSLR quality would basically cost as much as 2 dslr rigs
see these examples of DSLR vs all in one 360 cameras
IVRPA - The International Virtual Reality Photography Association is an international association of photographers who create and produce 360° Panoramas and other Virtual Reality Content including 360° Video, 360° Virtual Tours, Gigapixel Panoramas, and more.
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