I have used them for several years now, without any problems.... Opening one in ING was a lot quicker, I had to tell HSBC that I was a citizen otherwise they wouldn't let me create an account.

They are FDIC insured money market account, so they should be fairly safe, unless you are planning on depositing a couple of million dollars. But if you are reluctant, you can always get a 1 year fixed from your bank, which will give you 4.65% or so.

Cheers