I had one problem one time.
I pushed power button to start the reader, later I could not remember whether it showed a page for a fraction of a second or didn't show it all, but the screen stayed blank. No matter how many times I tried to switch it on nothing would appear on the screen. I thought that's it. I connected the reader to my PC via USB, then tried to switch it on and it worked! The reader was well charged, I think 3 of 4 bars. So, I disconnected the reader and it worked well since then.
The only worry it gave me that if I am traveling and I don't have a laptop and this thing happens....I would be in a big trouble.
What if it happens during a long 10h flight?
Otherwise, I didn't have any problems with the reader. I think I never dropped it