Well, I just upgraded my 2011 13" MBP and it is fantastic. However, I am not sure if your machine has SATA III - so you would not see the full speed potential.
Either way, the price is great, and your HD speed now is likely MUCH slower than what you would get with the 840 on SATA II.
Check out disk speed test from blackmagic and post your current read and write speeds.
R