Whats wrong with just using a round mold http://www.amazon.com/Ice-Ball-Maker-Premium-Silicone/dp/B00... ?

Quoting from bartender Jeffrey Morgenthaler's recent book:

> My experience using these has resulted in more than a few cracked ice balls, whose deep fissures essentially increase the surface area of the ice ball, negating any benefits in that department.

I had pretty much the same experience with my molds (I was using the Tovolo brand, rather than the one you linked to, though).

They work better with filtered and double/triple boiled water.

Or you could go for a pricier option such as http://www.wintersmiths.com/ (which uses directional freezing).

I haven't used one myself to confirm the quality, but Cocktail Kingdom (which comes highly recommended + I know from experience sells great bar products) has them for $150 for 55mm models and $300 for 70mm models.

Williams Sonoma is likely adding a huge markup.