Slower than class 4.
Its capacity is approx 29.8GB after FAT32 formatting.
I filled my card with data and then checked the integrity of the data and there were no errors, so that's good.
To write sequentially to the card until it was full took 2+ hours and averaged 3.25MBps which is slower than the class 4 MINIMUM of 4MBps. The read back averaged 14MBps.
The card performs better with files 50-100MBps and achieves the class 4 minimum near enough spot on.
If I were to say 3 stars would be "as described" with 4 being "better than expected" and 5 being "amazing". 1 star would be "useless" then the 2 star rating this gets should indicate that its not as good as it should be but it is "usable".
I've yet to try with any other file system.