Yep, it's definitely a 2 key rollover board, there's going to be some combos that don't work. Typically, if you're holding WD, 3 or 4 won't work, C won't work, etc, and if you're holding WA, then 1, Q, and Z won't work. I generally only noticed rollover issues in WoW and similar, while trying to strafe and move forward while using abilities, almost always in pvp. I ended up getting in the habit of always strafing left, and just mapping all of my useful abilities to 3 and up. It's not an issue for most fps games, but it's annoyed me several times trying to do complicated stuff in MMO's.
Like Ripster said, their advertising mentions "up to" 6 key rollover, but that could mean as little as a single combination of 6 works, like A F J L Esc Up, or something similarly useless. Any keyboard can do up to 6, what you're looking for is generally advertised as n-key rollover, which functions as 6 key rollover under USB.