Gle,
"I am quite impressed with how well they have been able to solve this technically rather difficult issue".
With respect, Gle, this is probably more a reflection of your lack of knowledge (which seems to surpass my relative lack of knowledge) on this subject.
"an exchange live feed is preferable" to confirm the SB's quote. This shouldn't be necessary.
No problem Grant, no offence taken. Earlier in my career, I have worked a lot with IT related issues, including software, hardware and Internet applications. So I know very well what I am talking about. I am well accustomed to the technical demands that are required, in order to present quotes in real-time on a live site. To recalculate the real market feed, including the spread, is not as simple as it sounds, when we are talking about speed and updates in milliseconds of financial information. This, in combination with security issues, makes it essential and crucial that everything works as flawlessly as possible. Superior speed handling and sophistication, both by the software application and by the hardware, such as servers is required, not to forget the site monitoring and the back office administration. Combined with the handling of maybe thousands of orders simultaneously, is asking a lot from the system and trading platform in question. In fact the whole financial industry is constantly asking for faster real-time systems in order to live up to an ever increasing demand for speed. I suggest you read up about RTOS (real-time operative system), and what impact they have on the financial industry as a whole, to get some idea what I am talking about.
When trading with SB you need an alternative and external source feed, just to be completely sure you get the correct quote. You have the real market feed that needs to be recalculated and the SB spread added, and then presented instantly and correctly on the site. This is a source of error, and should not be ignored. Even if a major misquote rarely happens, it might be a hard learned lesson to get caught up in one. When the real market moves in a highly volatile situation, you must be completely sure that the SB quote follows the movement to the point, without any kind of delay in synchronicity with the underlying instrument.
With DMA you also have issues to deal with, I have a friend who lost a fortune on a failing front end application (API). DMA is not the "Holy Grail" as many DMA traders portrait it to be, it is not completely hassle free. I am quite confident saying trading with DMA does not make you a better trader, but experience for sure will.