One word: fantastic. But don't take my word for it. Check them out for yourself.
Thanks DPReview for the great find.
9to5Mac: iPhone 6s and iPhone SE 4K Video
The above video is a testament to how far phone cameras have progressed. But what a random clutch of subjects and angles to choose in comparing video function of both phones.
Source: 9to5Mac - iPhone 6s vs iPhone SE iSight camera comparison
The next level of mobile photography
That's Relonch's tagline for their APS-C sensor iPhone camera add-on. While the copy reads like it came from a hat -- the next level of mobile photography is the smartphone, not an interface that enhances it -- the idea has merit.
Interfaces that work with existing hardware allow greater user freedom- certainly more so than unwieldy beasts, like the Panasonic Lumix CM1, a smartphone with a one-inch sensor and Leica-branded lens.
Relonch's 500$ price point likely will keep it out of the hands of binge purchasers, but its product location as an extension of, not replacement to, your smartphone is a step in the right direction.
Headfi: iPhone shoots the moon
Headfi super user, CN11, held his iPhone to a telescope eyepiece to obtain the above images.