The FPS Freek can help you improve your accuracy, but will throw off your timing for fast-paced combat. The Speed Freek doesn't seem to offer any improvement what-so-ever.
The FPS Freek will definitely help you with tweaking your accuracy, and on the PS3 it improves the feel of the rather small controller.
On the Xbox the FPS Freek pushes just beyond the comfort zone, and provides a reduced reaction time. The Speed Freek feels awkward, and doesn't seem to offer any benefits to game-play what-so-ever.
Over the last few weeks I’ve been feeding my need for action with a heavy portion of FPS and Driving games. During that period I opted to try out a couple interesting little products from the fine people over at Kontrol Freek. Those two being: the stick-extending FPS Freek, and the half-pipe-inspired Speed Freek. Each accessory is dedicated to specific needs for specific game types, but does adding $14.99 worth of plastic to your Xbox/PS3 controller make a world of difference?