We have had several Whisper/Wonder Mills, over a period of 20 years.
Before that we had a County Living mill. We had figured our children would enjoy cranking the thing, but.. not so much! It was harder to crank than any of us expected and was quite tedious when grinding all the flour for our large family. We then installed a motor on the Country Living mill, but it was still slow, and quite bulky to store with the motor mounted on it.
We ended up with the Whisper mill, and when the first one wore out at about 13 or 14 years, we got another one. (This was after grinding several tons of grain!) It was so much faster to just grind what we needed in a minute or two, rather than cranking for half an hour. The Country Living mill also needed to be re-sharpened every couple of years. (They suggest just buying a new set of plates, but it's much cheaper to resharpen with a sharp file.)
Our second Whisper Mill did cause some problems which would have been covered by warranty, but warranty in Canada at that time was not practical because shipping was our responsibility, and it was quite expensive. There is now a Canadian parts and service centre in Alberta I believe. We just kept that second one for parts. We have our third Whisper Mill now and it is holding up very well. I don't think the flour is any warmer out of the Whisper Mill as it was from the Country Living mill.