The heat (...which is a problem) in an HMD comes from the user's face and breath, and the screen itself does not radiate much more than light - it's not like it's a CRT (I'll say nothing about the radios on the device, though, nor CPU/GPU heat).
There is some eye strain with prolonged use, absolutely (the lenses come with a new problem, that has to be mitigated, for every one they fix; and until resolution gets high enough, we have the infamous "screen door effect"), but so there is with extended book reading. Actually, the HMD lenses makes your own lenses relax, to focus at an "infinite" distance, rather than a close one.
It can be hard enough for developers to support Mac and Linux - usually they don't have an installation set up, to test on. :P (It's still mostly an enthusiast developer base at this point. As such, though, they are at liberty to at least offer an untested and unsupported build, and just state that: "This may or may not work for you" - not that we'll see anything like that on the storefronts :7.
I don't know what you mean about a different shaped screen, or redundancies.
The Note4 screen is the same dimensions as the one in Oculus' Development Kit 2 (5.7" 16:9), is of the same type of technology, and has higher resolution.
The older Note3 display in the DK2 has a pentile subpixel arrangement (alas), and is overclocked for a higher refresh rate. I don't know whether the Note4 one does 75+Hz, nor whether it has full RGB pixels, (or whether it has yet done something about the "true black smearing" indigenous to Samsung's OLED displays so far), but it has to be an improvement at least in that it's 1440p over the DK2's 1080p (...and a likely candidate for Oculus' first Consumer Version).
It is certainly better than the light-leaky, image-retention-prone, lowres LCD in the DK1.
(The one inherent optical downside to the drop-in-phone solution, would be that the phone (and DK2) has the front glass, which can sometimes reflect the reflection of the screen in the lens)
"Cheap" as in "low cost", does not necessarily have to mean "low quality" - heck, Oculus themselves are talking about selling at cost and make their profits on software and services.
Besides; If you count the price of the Note4, the GearVR may not seem so cheap...
If one were to run with the attitude you suggested; Consider that at its core, the Rift hardware is just a screen, a skimask, two lenses, and a gyro - add your own computer.
It is the "getting it right" that makes the experience good, and Oculus seems to think that their involvment will help with that, here. There are other teams (not Sony), jumping the bandwagon, who do not appear to know what they are doing, and they are the ones who may sour VR for for somebody whose first contact is a sub-standard solution (...where "solution" is much more than just the hardware).
The deal was, as far as anybody can tell; "You give us preferrential access to your displays, and we share what we have learned and developed, to help you with a HMD of your own". The GearVR has its own high-update-rate calibrated IMU (accelerometers, etc), not relying on the ones in the phone, and the software and methods is what Oculus has come up with after months of experimentation (EDIT: ...for all that it is yet by no means perfected). (If this lets Oculus have Samsung construct custom, maybe suitably curved, screens for them, I'm all for it.)
The IMU offers DK1 level headtracking (i.e. only rotational).
If the screen's refresh rate is high enough for it to work without flicker being noticeable, the OLED display should, like DK2, offer low persistance mode (strobing the image, for smoother perceived motion)
... given this; The barrel distortion, with chromatic abberation correction, sensor fusion, motion prediction, and "timewarp" (late motion adjustment), should be just the same as with a Rift, as used with a PC, but without the positional tracking added with DK2; and with graphics complexity tuned down, to fit the performance of the hardware.
It will never be quite what you can do with a souped-up PC, but should still be quite compelling - heck; some were impressed with Google Cardboard and the many similar phone VR harnesses that went before it.
I'd imagine it mostly used, by a small number of people, for movie watching and casual gaming, whilst travelling (EDIT: In something that has a moves steadily and stably, or between trip legs -- use in a car should be a trip to vomit city. :P)
Future devices is another matter -- Even after all these decades, it is early days for VR.