Here is the low down on the Reactor series from fin guru Richie Lovett:
"The Reactor is a very upright fin, meaning it has a low sweep angle and therefore will make tighter, more acute directional changes. Not only that, having a more ‘upright fin’ reduces drag so the Reactor is considered one of the faster fins on the market. Think hollow waves and beach breaks where quick turns are on the menu. Basically, this fin lets you get vertical with minimal effort and will shorten the time between turns. The Reactor also has a smaller centre fin, which makes it easier to release the tail and kick the fins out of the lip, and for that reason it’s perfect for surfers who like to perform progressive turns. Lastly, a more upright fin like the Reactor is recommended for boards with moderate-to-low rocker".