So long as you're using the 85mm or 110mm version of this lens, you're spending $130-$150. This, of course, begs the question of whether it's worth it.
I would definitely say that the device is worthwhile, especially since the prism-setup inside allows you to white balance more easily than if you're trying to white balance off a white piece of paper or white card.
Moreover, having a single white balance device that you'll always use is the best way to make sure that your white balance is as consistent as possible. Let's be honest. Unless you paid $30-$50 for an industry color white balance card, you're probably currently white balancing off anything that's remotely white, from a T-shirt, to a piece of paper, to a bounce card. This can yield shifting hues of white throughout your shoot day. As such, having a permanent white balance card that's encased in plastic and hung around your neck via a lanyard is a great way to make sure you always have the same white balance item. It's simple to use and it has a more forgiving nature than other white balance items. Additionally, the fact that it'll pick up truer colors in mixed light environments may just keep you from having to do much (if any) color grading after the fact.
As such, the CBL is definitely valuable, I just think that $150 for the most popular 110mm version is too expensive. (Not to mention the staggering $600 price for the 220mm version!) I think $79.99 would be a much more reasonable price for the 110mm, with $69.99 for the 85mm and $149.99 for the 220mm versions. Hopefully the folks at CBL will reconsider there price-point, because lowering it a bit could make this white balance device a lot more popular with low-budget filmmakers.
Although the CBL system is pricey for what you get, it is very useful and helpful. Moreover, since most of the cameras that are popular with low-budget filmmakers tend to heavily compress their footage (especially HDV and AVCHD cameras), the more pristine the footage that you can capture without having to tweak it in post-production, the more pristine your final film will look. As such, if you have the extra cash to buy this lens, you'll find it a worthwhile investment.
