I cannot see the sensor size having any bearing on how it stores the images.
It's that 4k needs more than 10MB/s and it's a cheaper way than to insist on SSD drives. Not saying the system is perfect, just saying the sensor doesn't have bearing that they use 4 SD Cards. Though, the fastest recording speed seems to be 18MB/s, so going beyond 3 class 6 SD cards seems odd. Just seems like more can go wrong the more moving parts you rely on. For 1080p, you shouldn't be forced to continue to use multiple cards (if it does).
Actually, the compression rate is 36Mbps/card - read/write speeds do not correlate to compression ratio.
As Jax was saying, the sensor has some bearing on the quality of the picture being taken. The sensor seems rather small for a 4k camera. It's only slightly larger than what sensor you can find on a t2i/t3i/t4i. (Note, I believe the Red Cameras have a 4/3" CMOS sensor, so consider the approx 19:1 sensor size difference) Also, as Jax noted, not being able to change the lens could come to bite you on the ***.
t2i etc. are APS-C sensors which are slightly smaller than S35, but certainly a
hell of a lot larger than 1/3". REDs are APS-H sensors, slightly larger than S35.
I'm not 100% sure how the debayering works, but you can get 4k out of a 1/2" sensor, the same way you can get HD out of a 1/4" sensor. But, as I've said many times - spatial resolution doesn't mean all that much in terms of picture quality, and the fact that you can have 4k on a 1/2" sensor kinda proves that - you'll get better images out of a native 2.5k raw BMCC than a 4k compressed 1/2" sensor JVC. I shot on an FS700 recently, which isn't as compressed as a DSLR and has a S35 sensor, and it looks horrible on a big screen - not as bad as a DSLR, but still pretty bad. I'd be interested (and probably horrified) to see this JVC's images on a big screen.
That all being said, it's way better than what I personally have. It's a complete 4k package that can do the ratified 4k standard in 60p, 50p and 24p, or 1080p. It doesn't seem to be able to do 720p though. Apart from the 4 SD card thing, I don't see it being that horrible if you don't have access to a better option.
Max 2 hour record time on
four 32GB SD cards. Assuming you're already used to a DSLR setup, perhaps you could get away with it, but the issue comes that if you need to shoot more than 2 hours full res, you don't need one SD card, you need
four. Those who are used to carrying around 5 or 6 SD cards just in case for their DSLR shoots will now need to carry around 20-24 SD cards proportionally.