Product review (4 stars): Makes Ice Fast, but not a lot, portable (110 Volt, not batteries)
The ice cubes are not completely hollow, but partially hollow, bullet shaped.  If you make about 1/4 to 1/3 gallon of ice (by volume) the basket where the ice is kept fills up and it stops making more ice until either you take some out, or until some of the cubes melt.  When the level of the ice in the holding basket gets low then the ice maker starts making ice again, automatically.

The ice in the basket is held in a small refrigerated area, but its not completely cold enough to keep the ice from melting, so the ice melts slowly if you don't use it.  The water from the melting ice  goes right back into the water reservoir to make new ice.  I guess if you never took the ice out of the basket, it would all melt back into the water, then be made into cubes, and melt, forever (wasting a lot of electricity along the way).  By the way, this does not run on batteries, and not on a 12 volt car outlet, it needs a 110 volt wall plug.

Because the freezer area where the ice is held in a basket is not terribly cold, the ice is a bit watery, and soft.  I happen to like softer ice, so thats not an issue for me, but it melts faster in a beverage that way too.

Three issues to be aware of 

1. This thing is a bit loud in more ways than one.  Its a small refrigerator, with a small compressor, a fan, and ice making stuff inside it, and its not all that insulated.  When ice falls into the plastic basket, you hear this and it gets annoying.  We have a real ice maker in our upright freezer, and you hear the ice in there too, but its more insulated.
2. The instructions say to NOT pour the water out of this.  But rather drain it out of a little drain in the bottom.  So, if you use it, and then want to put it away, your instinct tells you to pour the un-used water out, after all its not that big, so you want to just tip it over a sink, right?, but NO, they say NOT to do that (I don't know why) but to drain the water out the bottom, and that little drain is a bit of a pain.
3. This thing has a lot of plastic, and smells like plastic, and at first, the ice smells and tastes like plastic.  You will need to make a few (they say a few, I say a weeks or more) of ice through this thing to get that smell mostly away.