Note: The link from dooyoo seems to go to a Komputerbay SD card, which is way overpriced. This link goes to the corresponding memory card. Also Sandisk have stopped doing class 2 versions of this, so the one from Amazon UK will in actual fact be a Class 4 card :) http://www.amazon.co.uk/dp/B003HIWHN0
I bought this card for my Galaxy S2 due to the fact that it's read and write speeds for small files is faster than most. Transfer speeds of big files like videos and MP3's are really quick, but its normally hard to find a memory card that can transfer tiny files (400kb and below), such as game and app installation data fast. This card can read and write these small files extremely quick though. This is beneficial if the memory card is being used on for example Android devices, that have games and apps that install data files which vary in size. It also means that apps on the external sd card load up really quickly, whereas on cards that can't transfer small files quickly, apps will load much slower.
** The following is an extract from XDA Developers. They are one of, if not THE biggest modding forum for Android phones and I've learnt a lot about Android phones just by reading information from their site **
"My recommendation after playing with all sorts of microsd cards and speeds is to get a sandisk 32gb card class 4.
Why this recommendation?
Randrom read write is the most important for speed during normal phone performance and i have seen sandisk cards have it the highest.
HERE IS A POST FROM SOMEONE IN XDA. Forgot the source:
Class 2 and 4 cards have better random access speed and random read/write than class 6 or 10 cards in general. To get higher sequential write speeds, manufacturers sacrifice the random access speeds. That's just how it is.
The best all around card I've ever found is Sandisk class 4.
My 32gb Sandisk class 4 outperforms any other class 10 or 2 32gb card I've tested in the random access and random read/write speeds. That's what's most important when using with WP7 or Android when using it for apps or OS files that need to be accessed quickly. Class 6 and 10 cards are setup to initialize the area of the card that is about to be used to make the sequential write/read quicker, but it takes extra time in the beginning to do the initialization. If your using the card where you need to access small bits of info from various parts of card quickly, you will do best with class 2 or 4.
Most people seem to assume that the higher the class, the better the card is for everything, but that's not how it is. Different purposes need different kinds of speed... cards with higher sequential speeds have lower random speeds."
If your merely purchasing the memory card for an MP3 player then I doubt you would complain with the performance of this memory card, but there are faster cards (Like class 6 or class 10 cards) which could be bought. However for all round performance, and for its price, I can hardly recommend something else. It loads apps quickly. Recording HD video is quick and I've never had an issue recording straight to the SD card. And it transfers files pretty darn quickly as well.
UPDATE: Here is a list of normal read write speeds and random read write speeds. Once again, random speed is better for loading apps and OS files. Normal write speeds will be more beneficial for large MP3's for example.
Normal R/W: http://img847.imageshack.us/img847/5071/screenshot20110611at120.png
Randow R/W: http://img30.imageshack.us/img30/5071/screenshot20110611at120.png