I bought these triggers after having used them at a friends house and they do certainly make a difference to how fast you can fire and your trigger reaction speed. However, I have owned 3 pairs of these in the last 6 months due to them cracking or the clips which hold them on falling off (I do not advise continuously removing them and putting them back on as this wears away the clips on the inside). Thankfully, Amazon's wonderful customer service happily replaced mine each time they went wrong, but it is still very tedious.
Due to the disposable nature of these, their cost is fair enough. They are only designed to be a sort of throw-away item and definitely do improve gaming performance when needed most. But after my 3rd pair broke, I gave up and bought EA Sports: Comfort Play Pack with Game Grip Technology (PS3)
for £5.99 in GAME. This product is much better quality, being a mixture of rubber and plastic and not just plastic (and the reviews are great).
Noticeably better and more comfortable for long gaming periods
Stay on well
Look good, match controller
Cheap and cheerful
Can take some time to get used to
Clips which hold them on can wear away
Break/crack easily if dropped or after some time
These triggers are great for what they do, but don't last long enough to be a worthwhile purchase. I wouldn't advise against buying them, but if you do and like them, but then they break, invest in the EA Sports Comfort pack, for triggers and grips that will last.