I have'nt used Halo finacial, but the other main player in the currency transfer marjet is moneycorp.com. I and several people I know have used them and their service has been great. They offer a better rate of exchange than banks and no commission, so will save you thousnads if transfering a big sum.
I have not used Halo either. However, I recently used worldfirst to transfer money to Canada, and they offered the best rate. I looked at five companies and world first (at the time), had the best rate.
Also, the rate companies offer you varies hugely depending on the amount you want to convert. Playing one company against another always seems to help, as their rates are flexible (they don't normally advertise this fact).