ChromeOS isn't great, but the hardware offers a great mix of performance with low size and cost. The push to get them into educational environments also means that they often prioritize things like spill-proof keyboards and shock-proof chasses. And they also usually have fairly good physical security; most of them have a screw on the motherboard that you have to open the device and remove to reflash the boot firmware.
Like I said, the main difficulty with iPads is that you don't get many options for what you run on them.
And as for performance, I use mine for development and EDA, and speed has never been a huge concern over the years. I even get a reasonable 40fps when I'm working on my toy 3D game engine. Just because they ship with bloatware doesn't mean they aren't real computers...