STK - Nasdaq commission question

["Gene K. Frydel" <Gene.Frydel@xxxxxxx>]

Fellow Traders,

I stumbled upon an advertisement for a stock broker offering zero
commissions on Nasdaq trades of at least 1000 shares.
They're at http://www.webstreetsecurities.com

My question is, how do they make money on those trades?
Also, does one pay extra in the form of slippage, and
has anyone had any experience with them?

Thanks,

Gene