Bought it for $300, letting it go for half the price, you enjoy it, I don't need it anymore!

The Helix MagLock™ Filter System was developed to both eliminate the hassle of threading filters on and off, while also providing a filter that's safely locked in place once installed. Unlike other magnetic filter systems on the market; Helix provides a completely secure connection using our magnetic + quarter-turn locking mechanism, making it lightning-fast to install/remove filters while also ensuring they stay locked in position during the most demanding shooting situations. Seriously, these filters won't go anywhere until you're ready to remove them from your lens! With available 67, 72, 77, and 82mm brass thread bases, Helix will easily cover your entire lens arsenal.