Kontrolfreek.com sent me over a set of Speed Freeks and FPS Freeks - control stick add-ons that are said to aid in your success in certain games. 
First off, what are they?
FPS Freeks - Control stick extenders that clamp onto the top of the control stick making them almost twice as long giver you a finer level of control over the stick’s movement. Essentially using the theory of a longer lever gives more power.
Speed Freeks - For those whose thumbs don’t alway stick to the control pad. These C-shaped plastic bits clamp onto the control pad head to help you waggle the stick without as much pressure or fear of losing grip.
Alright, so you’re up to speed on what they are. So now let’s look at whether or not they work. I’ve tested them on both the PS 3 and Xbox 360 but mostly on the latter. So I’ll generally talk about that.
I’ve been testing these for some time because you sort of forget that they are there. But I started playing Blur and thought that I 
might like some finer control on the left stick (the steering stick) and switched from the Speed to the FPS. That made me realize a serious drawback to the Speed Freeks - they may damage the head of your control stick. The claws on the clamping mechanism for this particular product gouged into the soft rubber coating of the stick to the point where some of it is now cut and/or missing. Certainly a caveat emptor - buyer beware for this product. Because it could irreparably mar the edge of your control sticks. It was most likely from some recently heated FPS action in AvP or else when I was racing in Blur.
Another problem with the Speed Freeks is that there is a rather sharp edge on them and it will eventually dig into your thumb if you’re playing something hardcore. That was another of the reasons I wanted to switch to the FPS for Blur. I’m not saying that the Speed Freeks are bad, just that there are some design issues that really need improving. Luckily, I have like six X360 controllers and can switch to one that’s not scarred if I want, you might not be so fortunate.
On to the FPS Freeks. These use a similar clamping system made of hard plastic and sort of snap onto the top of the control stick. They grip extremely well and I had a small struggle to get it off and check to see if it too had marred the control stick. It hadn’t and upon closer inspection I saw that the clamps on the two are slightly different. The FPS has a thicker more solid clamp than the Speed which seems to rely on a thinner c
lamp with a noticeable edge. That is obviously what cut into the rubber on the stick.
Now I fired up Blur (because that’s my game of choice this week - the multiplayer demo) and got down to it. I had played a few hours last night with the Speed and wanted to test out the FPS. The results? A first and a third in two races. Granted, I’ve now won 6 of 20 races so I’m no slouch in racing games, but it certainly did feel like I had a finer control over the car’s steering thanks to the longer control stick. I will most certainly continue to use the FPS Freek on the left stick of the Xbox 360 controllers and might even use the other on the PS3 for some games there. The nice thing is that even though they can be a bear to get off, you could switch as needed.
The truly ironic thing here is that the Speed Freeks are designed specifically for racing games and "allow you to hug the turns." However, because of the edge on the thing I found it less comfortable and prefer to use the FPS Freeks (and not the Speeds at all now) for all sorts of games.
How does it work? (from their site)
FPSFreek was developed to improve your accuracy in first person shooter environments, helping you react and hit your targets faster. FPS Freek extends the length of your analog stick, increasing your range of motion, giving you 40% more linear distance from full stop to stop.This gives you more leverage and increased control without disturbing your natural gaming feel. 
FPS Freek will help you to aim and lock in on your target faster, while putting less strain on your finger.
SpeedFreek was developed to give you more control in racing games, enabling you to improve racing times when running against the clock. The unique curve of SpeedFreek enables you to hug the turns in racing games, without your fingers slipping off the controller or creating unnecessary friction on your fingers. SpeedFreek keeps your thumb on the existing control surface, with no disruption between the natural geometry that you have learned to use. SpeedFreek’s supporting side walls enable sharper movements while adding to your control and precision in racing games.
The final results:
I would not suggest the Speed Freeks until the issues mentioned are fixed. They need to round the corners on both the edge of the unit where your thumb rests as well as fix the clamping mechanisms to keep them from potentially damaging the rubber around the control stick head.
The FPS Freeks, are pretty cool and I think actually do give some serious fine control thanks to the extended range of motion. They’re solid and comfortable with a concave thumb surface and some ’grip dots’ to keep your thumb from slipping off. Definitely seem to have improved my performance slightly in some games. I’ll keep using them.
Speed Freeks: Skip for now Overall: 5.0
FPS Freeks: Might help you get a little more out of your game. Overall: 9.0
