Worldspreads zero spread

I knew it wouldn;t be long before this came to the market. Worldspreads are no offering zero spread on major instruments (only 8 of them like FTSE, EU, AU, etc.) with a platinum account.
Any ideas on their platform whether there is slippage or not? I might try a demo.
Would have been nice to see zero spread on US instruments and GU as well.

already discussion, SM - see http://www.trade2win.com/boards/spread-betting/102966-zero-spread-worldspreads.html