That's interesting as we are actually having the opposite to your experience in the school I work at.
The teachers (mostly) think they are great
Before students had these devices they had pen and paper. Now they have a device that does word processing, spreadsheets, basic multimedia, communication (email, video chat etc), has access to a wealth of information through the internet for research, access to our online learning environment and more. A lot of activities that are great for education across every subject and that they couldn't do prior with pen and paper. And it does all these activities rather well and because it is low powered it easily lasts a whole day without recharging (with the model we have). This last point is really important as it alleviates the problem of a mess of cables for people to trip over etc but it also allows people to move around a lot easier than when they are tethered which is good for collaboration exercises.
Of course it doesn't do cad and multimedia and all that other fancy stuff. That is what our labs are for and in our opinion a desktop with a 20 something inch screen and a mouse and that is plugged into power permanently is much better for doing those tasks than even a high end laptop.
Actually you can do cad and multimedia and a lot of that other stuff on these devices. There are web based options for many of these things. Sure they aren't as powerful but for teaching the theory and concepts you shouldn't need the full blown tools (unless you are a poor teacher who doesn't understand the theory and concepts well enough and can only teach a product which you yourselves were taught on.) For instance we teach students cad with Tinkercad.com and they easily transfer those skills over to AutoCad in later years.
From a management point of view they are awesome. Way fewer breakdowns than with traditional laptops and when they do, a lot of the time a Power Wash and the student is back up and running in a matter of minutes. If it's hardware we loan them another device, they log in and are off and running again in a few minutes, and again when they get their repaired device (or a replacement) back.
I really hate this argument that a device that is easy to manage and offers many things they didn't have before (with just pen and paper) which are of value and which this device does really well, and is actually quite well priced, is useless because it doesn't do some other things which are specialised and for which we already have better devices doing those tasks anyways.