I have used one and would not buy one!!!

They really do work as well as the video shows with most wood, both hard and soft, both thawed and not... But
and this is a big, big
BUT

I would rather put a zapstrap on chainsaw triggers and juggle them running wide open... blindfolded, than use one of them.
You see in the video how they chip off pieces off the side of big logs???

yup does just that... but if you do not have a measured stroke (just hard enough to break the log), the ax kicks out the side and flies dangerously close to your leg, while lying the log on its side. Additionally, when it rotates to the side to kick off the chunk, it either twists out of your hands (hardwood) or wrenches your wrist... again and again and again...

I split a lot of wood, and when I have to do it by hand(check the 'I am outa here' thread, it is with a wedge and a sledge. fast easy safe.

If you want a gimmicky splitter that really does work, try one of these: