A thing to clarify - the SATA 1.5Gbps and SAS 3Gbps limitation was the initial spec of the card. At some point, a firmware update unlocked the full SATA 3Gbps and SAS 6Gbps mode. Do a search for them online, hardforum.com has a huge thread about them.
You will be able to update the firmware most easily if you have an HP system (or atleast a compatible HP SmartArray card, such as a P410). You can look on that forum to see what other people have done with them.
I run one in a DL370 G6 and have had good results with it. It is supporting a mix of SAS and SATA drives with no problems, but I have not verified the speeds. Coupled with the integrated P410i array and a 1GB FBWC module, it screams for my purposes as an all-in-one home server/test bed. Of course, my system was meant to take that expander, so YMMV in a different setup.
I paid $60 for mine a few months ago, but it came with 4 of the HP SFF-8087 cables. If you don't need those, this looks like a decent deal, about the same as you can get regularly on eBay. Sometimes they come with a plastic bracket on the back for cable routing; I found it handy and it relieves the stress on the ports on the card.