I'm not sure why, exactly, this is so fascinating for my kids - after all, there are plenty of educational videos out there - but it is. I downloaded it to my phone months ago and forgot about it, until one day my kids discovered it. We had to put it on their Kindles so I could get my phone back. The older two ultimately offered to pay for a subscription with their allowance so they could watch older movies no longer available in the free app.
As mentioned, they have movies on a huge variety of topics, and all are handled very well from my perspective - even items on potentially tricky topics like pregnancy and September 11th. It's also good at explaining somewhat complicated concepts clearly (like heredity, or even compound interest!). Because of this, I personally plan to use it to start our discussion when my kids ask questions on topics that are hard for me to explain.
And my kids would spend hours watching it if I would let them. Even the four-year-old enjoys it, though I am sure that the content is mostly above her level. Overall I highly recommend it.