Now the same company has launched a clear ice ball maker and they sent me one to test out. So that's what I did.
Long story short: It worked great on my first trial, but not every time.
The Polar Ice Tray works just like the directional freezing method of making clear ice balls (read about that here or all the ice experiments on Alcademics here): The container is insulated on all sides but the top is not. The ice freezes from top-down, pushing trapped air and impurities downward.
What this product does is offer an easy way to get the water into the molds and the balls out afterward. It's shaped like a little tug boat.
The outer blue container is just softish foam. Inside there is a top and bottom half of the ball mold (this model comes with animal shapes that are pressed into the top), and a bottom water receptacle.
The bottom half is perforated so the cloudy part is pushed into the receptacle. To use it, you fill water in the little spout and then let it freeze for a day. Here it is after freezing.
The cloudy part of the ice is on the bottom.
Now for the big reveal.
It is super easy and the spheres are nice when they come out perfectly. It may be more space efficient than the insulated mug method for two spheres, depending on whether your freezer offers more horizontal or vertical space.
However, on subsequent uses, I've found the tray can separate during freezing, spilling water out the sides and making incomplete ice balls - only partial spheres because the water has leaked out the sides. So you need to make an effort to get a really good seal on the different parts that fit together. I tried and still failed twice.
So far I've used the tray 10 times and 7 of those times it worked and 3 times it failed. (For the record the insulated mug method has never failed me.) If I discover a good way to ensure a seal I'll update this post.
The tray is a bit pricey at $55 plus postage, but I spare no expense for ice! You can buy them on the Polar Ice Tray website.