I tried one. It lasted just long enough for one job, and nothing since.
I think it was probably just a case of fragile USB and micro-USB connections not being reliable enough, when you get a tablet joined to an 'on-the-go' lead, joined to the scope. In my case, the LEDs that should illuminate the subject stopped working and I've not been inclined to spend more time fiddling with it. (A 'proper' webcam without illumination worked first time on the same lead.)
I can save you some time though - ignore any mini CD or driver download that comes with it, unless you love updating drivers and following poorly translated instructions. Just install CameraFi from the Play Store and use that to display or capture the images.
Overall, they are so cheap that the risk is small, and they can make otherwise impossible jobs practical.