First, I'll put DSLRs and mirrorless cameras in the same category -- serious interchangeable lens cameras.
Second, smartphone cameras are putting a serious dent in the DSLR/mirrorless market.
Where do I think this will lead? The market for the DSLR/mirrorless will go to not quite zero. There will be less profit motive for the camera companies to produce new models and, maybe, some companies will get out of the business, just as HP got out of the photo printer business. There will be occasional new and improved models and they will be significantly more expensive than they are now. But there will always be a few of us hardcore photographers to prevent extinction.

Yes, you can "use" it with film also, color negative or positive.

The issue is that it does not work on a JPEG in conjunction with the eyedropper in Capture One - probably any other raw conversion program.

Taking measurements with the eyedropper on a JPEG image does not work on all of the gray scale squares as well as it does for a raw file.

Clicking on the six squares from white to black produced different color temperature settings - 7391k, 11555k, 12828k, 13802k, 14000k and 14000k. Those are not real color temperature values. The tint results were all over the place after the third square. The only reasonable result comes from the second square.

Ideally we should be setting the white balance as we convert the raw file.

But unless there is something deficient in ON1, the eyedropper can work on the JPEG. Here is the result from Capture One.

I clicked on the second white square in the Color Checker and ended up with 11417k@-3.4 tint. I wasn't so lucky with the other squares. But that is not a raw WB. It's the Capture One setting for adjusting the JPEG. It's on a different scale than the one intended for raw and does not line up with the color of the light.

Then I clicked on the white collar of the guy on the can and got 11600k@-5.5 tint. But the collar is a very small target and the result depends on where exactly I click because it contains a lot of noise.

I could not tell the difference between the two results on my calibrated monitor.

Two takeaways:

1. The WB needs to be set with a bright white area in the JPEG and you should avoid noisy areas. Your Styrofoam container should work.
2. The color checker is designed to be used with a raw image. It won't work well with a JPEG.