I tested a 520 Series recently, they're not bad, though quite a bit slower for sequential write than many
other models, but the price was very good, I got a 240GB unit for 48 UKP. Feel free to download my
results archive which contains screenshots of numerous tested models for AS-SSD, CDM, HDTachRW
and ATTO.
However, there are plenty of other options, eg. the ARC-100 (better write performance), various models
from Crucial, etc. I like the M550, but it's hard to find now.
Alternatively, just pick up a used Samsung 840, EVO or Pro off eBay, lots around atm.
Ian.